All optical multiplexer

ABSTRACT

Optical system ( 200 ), which controls interference pattern ( 150 ) of combined grating ( 100 ), by controlling different illuminations of beams ( 132, 134 ) on grating. Optical fiber ( 202 ) guides and emits used in optical communication. Information carrier beam used in optical communication. Information carrier beam used in optical communication. Reflector ( 206 ) receives beam and reflects beams toward attenuator ( 208 ), which transmits beam toward transparent blcok ( 104 ). Beam enters block without direction change and propagates in block toward grating layer and grating.

FIELD OF THE INVENTION

[0001] The invention relates to optical communications and moreparticularly to the modulation and switching of data on optical channelsusing physical effects involving the combination of energy in lightbeams in various ways.

BACKGROUND

[0002] In the field of optical communication, there is a pressing needto improve the capacity of optical networks and the speed of switchingat reasonable cost. These are attended by the related problems ofefficient retrofit to existing infrastructure, ease of maintenance,reliability, etc. The physical media of optical fibers used in currentgeneration optical networks have a tremendous as yet untapped reservecapacity. The reasons for this involve various bottlenecks, chief amongthem, the slow speed of switches for optical data. To switch opticaldata, either the data on an optically-modulated signal must be convertedto electrical modulation and switched by electrical switches or slowmechanical switches must be used. Even the latter involves the slowconversion of optical modulation into electrical signals for control ofthe mechanical switches. To compensate for the slowness of theconversion and switching processes, substantial parallelism must beintroduced into the design of switches resulting in high cost. In eithercase, currently, there is no analog to the network switches used inelectrical networks, where switching introduces minimal delay in thepropagation of network signals.

[0003] In addition to the switching process per se, the process ofgenerating optical signals—the modulation itself—is slow because of therise and fall times of current optical modulators. As a result, symbolsare much longer than need be, thereby limiting the bandwidth to a levelsubstantially below the potential of the optical media.

[0004] A technique called Wavelength Division Multiplexing (WDM) and arefinement called, Dense Wavelength Division Multiplexing (DWDM) arecurrently used to increase the capacity of optical media using currentmodulation technology. WDM or DWDM methods increase the transmissionrate by creating parallel information channels, each channel beingdefined by a different light frequency. Another method, Time DivisionMultiplexing (TDM) exists in which multiple data sequences areinterleaved in time-division fashion on a common medium.

[0005] WDM or DWDM methods increase the transmission rate by usingparallel information channels. The information in each optical channelis carried by a different light frequency. The light frequencies of thechannels are combined together and are inserted into the input of asingle optical fiber. The combined light frequencies at the output ofthe fiber are separated into different parallel channels, one for eachspecific light frequency. Although DWM and DWDM has the ability increasethe capacity of a fiber, the number of channels that may be defined hasa practical upper limit because of the limited bandwidth of the fiber(optical properties are attuned to a narrow range of frequencies) andbecause of the ability of the laser sources to contain their energy invery narrow frequency bands.

[0006] In TDM, the bits of several parallel channels at the same lightfrequency are interleaved in a predetermined periodic order to create asingle serial data stream. This method is very effective when using abuffer, which accumulates and compresses the data of several channelsinto a dense serial data stream of a single channel by reorganizing thisdata with suitable delays. However the data rate permitted by thismethod as well as others is still limited by the data rate and dutycycle of the light sources (DFB and DBR lasers) themselves. That is, indirect modulation, the power to the laser is switched on and off. Therate at which this can occur has a physical upper limit due to therelatively long recovery time of the lasers and it produces chromaticdispersions due to broadening of the emitted spectral line of themodulated lasers. This is caused by spontaneous emission, jittering, andshifting of the gain curve of the lasers during the current injection.Where modulation is performed in an indirect manner, the lasers areoperated in a Continuous Wave (CW) mode and separate modulators performthe modulation of the beam. The modulators are usually made frominterference devices such as Mach-Zender's, directional couplers andactive half wave-plates combined with polarizers and analyzers. However,an electro-optical must be activated to modulate the beam; to producephase shifts and polarization changes. Such changes involve the creationand removal of space charges, which change the density of the chargecarriers within these electro-optic materials. The formation rate of thespace charges is mainly dependent upon the speed and the magnitude ofthe applied voltage and can be on the order of sub nanoseconds. Thecharge removal is usually slower and is mainly dependent upon therelaxation time of these materials (lifetime of charge carriers) and canbe relatively long. Accordingly, the width of the pulses and the dutycycle of the modulation are dependent limited by the long off-time ofthe modulators.

[0007] These same rise and fall time limitations impose similar limitson the abilities of switches to direct light along alternative pathwaysaccording to routing commands and data. At present, there are two majorclasses of optical switches. In one class, optical signals are convertedto electrical signals, routed conventionally, and optical signalsgenerated anew at the output. As discussed above, the process ofconversion is slow and involves many parallel channels making suchswitches costly as well. This class of switches goes by the identifierOEO, which stands for optical-electrical-optical. A second class ofswitches goes by the identifier OO, which stands for optical-optical. Inthese switches, no conversion of optical signals to electrical signalstakes place. Instead, the optical energy is routed by means of some sortof light diversion process such as a switchable mirror. In one system,micromechanical actuators or so-called MEMS motors are used to movemirrors in response to electrical routing signals. The speed of suchswitches is again limited by the need to process electrical signals andthe slow response of energy conversion in the MEMS motors. The result isa need for multiple channels to be provided and great expense as well asdelay in the speed of the signals along the selectable data routes.

[0008] At present, the highest bit rate that can be achieved is about 10G bits per channel, which is limited by the modulation rate of themodulators, the pulse width that they produce, and the switching time ofthe electronic switches.

[0009] As a result of the foregoing limitations of the prior art, thereis a need for reliable mechanisms for exploiting the physical potentialof fiber optic media in terms of data rate, switching, and cost.

SUMMARY OF THE INVENTION

[0010] An all-optical system for modulating, switching, multiplexing,demultiplexing, and routing optical data employs control units thatdirect light energy according to a coincident control signal which isalso in the form of light. In an embodiment, a control unit directs asubstantial fraction of the energy (and included symbols) in a datasignal to a first output when a light control signal is simultaneouslypresent at a control input of the control unit and to a second outputwhen the light signal to the control input is absent. That is, when thecontrol signal and the data signal are coincident at the respectiveinputs of the control unit, most of the data signal energy is directedto one output and when the control signal is noncoincident with the datasignal, most of the data signal energy is directed to another output.According to an embodiment, this “coincidence-gate” behavior is broughtabout by the interference of the control and data signals. Note that thecalling one signal a control signal and the other signal a data signalis, at least in many embodiments, purely an arbitrary choice and is usedin the present specification heuristically to facilitate the descriptionof the invention.

[0011] In an embodiment, the interference of light in the control anddata signals is the result of applying one signal to a first diffractiongrating that generates a first interference order diffraction patternand the other signal to a diffraction pattern adjacent or interleavedwith the first such that a different interference order is generatedwhen both signals coincide on both gratings. In an example, the firstgrating may be a transmission grating with (broken) reflective surfacesbetween the transmission apertures defining a reflection grating. Withsuch a device, one signal may reflect off of the reflective grating andthe other signal may pass through the transmission grating. Thereflection and transmission diffraction patterns of either signalproduces first order diffracted radiation when only one signal falls onthe device at given instant of time. But when both fall on the device atthe same time, so that the effective pitch of the diffraction gratingincludes both the transmission and reflection grating, a lower orderdiffracted radiation results. In the case of the first order pattern,the lobes have different directions and/or intensities from that of thelower order diffraction pattern. With suitably spatially-locatedreceivers, the energy may be directed in different directions from thistype of interference device depending on whether the two signals arecoincident or noncoincident. The coincidence gate may thus have acoincidence output to which energy is sent when the both inputs receiveenergy at the same time and a noncoincidence output to which energy issent when the inputs receive energy at different times. Note, as shouldbe clear to a person of ordinary skill, for the above interference typeof coincidence gate to work properly, the phases of the inputs should beproperly aligned to insure the energy from the gratings falls on therespective receivers.

[0012] Preferably the first and lower order diffraction patterns arefirst and zero order diffraction patterns to minimize the number ofenergy pickups. That is, the effective number of lobes increases withthe ratio of the pitch to the wavelength. This makes it necessary toprovide more pickups to collect most of the energy in the lobes as theorder increases. To achieve this in the case of a grating, thewavelength of the light should be in appropriate ratios to the pitchesof the transmission/reflection and combined gratings, as may bedetermined by relationships well-known in the art. Generally, this willbe achieved by choosing a low order grating.

[0013] Using such an interference device as described above, by suitableconstruction of an optical device, incident energy is directed alongdifferent paths depending on whether the data and control beams arecoincident on the inputs to the interference device or noncoincident.The result is a basic component, mentioned above, called the coincidencegate. This gate may be used to control the path of a data signal. Forexample, by articulating a single data signal so that it contains pairsof pulses separated by a predefined spacing, and splitting this signal,sending one to one input of the coincidence gate and sending a delayedversion to the other input of the coincidence gate, the signal will betransmit a pulse at one output of the coincidence gate when the pulsespacing matches the delay and through another output when the pulsespacing is different from the delay. By sending such a pulse to a numberof different coincidence gates, each with a different delay, thearticulated signal will only produce a pulse at a selected output in thegate provided with the delay matching the spacing of the pulses in thesignal. Thus, the optical signal carries a symbol (the pulse spacing)that selects which coincidence gate-device its energy will be sentthrough. This effect amounts to a basic switching function. Note thatthe switching function can be layered by providing each output toanother set of different gates each with another different delay. Toarticulate the signal for successive layers, each pulse pair must bedefined by a pulse pair. This signal construction must be repeated, infractal-fashion, for every switch layer involved because each pulse paironly produces a single pulse at the output. The details of this processare described in the Detailed Description section along with supportingillustrations.

[0014] The coincidence device may also be used to create a modulator forsignal transmission because of its rapid on-off response. That is, iftwo broad pulses are applied to the control and data inputs of acoincidence device with different time delays, the width of the pulseemerging from the coincidence output will be determined by the periodduring which both input pulses fall on the grating at the same time.

[0015] The coincidence effect can be used to generate pulses that arevery narrow. By combining multiple ones of such pulse-shaving devicesfeeding into a common optical channel, very dense streams of narrowpulses may be generated thereby increasing the bandwidth of an opticalsignal. A mirror-image process can then be used to generate data streamswith larger pulse spacing along multiple channels at a receiver. Thus,the above description embodies a multiplexer/demultiplexer combination.

[0016] The above-described diffraction grating device is only one of anumber of alternative interference devices that may be used to create acoincidence device. A very similar type of device formed from waveguidesmay be used to produce diffraction patterns from control and data inputswith spatially-separated receivers. In addition, Y-junctions,directional couplers, fast-pitch diffraction gratings, beam splitters,for example, may be used as the bases of non-diffraction interferencedevices to produce a similar coincidence function. Examples of suchdevices are described in the Detailed Description section below alongwith supporting illustrations.

[0017] Also, in addition to the modulation and self-switching functionsdescribed above, the coincidence gate may be used as the basis for aswitch controlled by an external control signal. Thus, a data signalfrom one source can be directed to an appropriate output of a layer ofcoincidence gates by sending an appropriately-timed control pulse to allof the gates. Alternatively, a single selected coincidence gate can haveone of its outputs selected by an external control signal bytransmitting a control signal to only the selected coincidence gate.

[0018] An additional layer of symbology may be added to an opticalsignal which may be used for switching purposes in coincidence gatesemploying the diffraction phenomenon. The propagation directions of thevarious diffraction orders may be varied by imposing different phaserelationships between the data and control signals. By placing receiversin different locations, each set with different outputs, the coincidencegate may be configured to provide selectable outputs depending on thephase relationship between the pulses.

[0019] The invention will be described in connection with certainpreferred embodiments, with reference to the following illustrativefigures so that it may be more fully understood. With reference to thefigures, it is stressed that the particulars shown are by way of exampleand for purposes of illustrative discussion of the preferred embodimentsof the present invention only, and are presented in the cause ofproviding what is believed to be the most useful and readily understooddescription of the principles and conceptual aspects of the invention.In this regard, no attempt is made to show structural details of theinvention in more detail than is necessary for a fundamentalunderstanding of the invention, the description taken with the drawingsmaking apparent to those skilled in the art how the several forms of theinvention may be embodied in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIGS. 1a and 1 b are illustrations of certain principles of opticsinvolved in the operation of a diffraction grating-based embodiment ofthe inventions disclosed.

[0021]FIGS. 2a and 2 b are illustrations of certain principles of opticsinvolved in the operation of transmitting and reflecting gratingscombined together, in accordance with an embodiment of the inventionsdisclosed.

[0022]FIG. 3 illustrates an interference pattern of a combined gratingutilized in certain embodiments of the inventions disclosed.

[0023]FIG. 4 is an illustration of an interference pattern of a combinedgrating irradiated from two directions for purposes of explainingcertain embodiments of the inventions disclosed.

[0024]FIG. 5 shows interference patterns of the combined grating withdifferent illuminations for purposes of describing certain principles ofoptics involved in the operation of certain embodiments of theinventions disclosed.

[0025]FIG. 6a illustrates the controlling of the interference patternsof a combined grating for purposes of explaining certain principles ofoptics involved in the operation of embodiment of inventions disclosed.

[0026]FIG. 6b is an illustration of all-optical switching of aninformation carrier-beam between ports using a control beam according tocertain embodiments of inventions disclosed.

[0027]FIG. 7a shows additional all-optical design for controlling theinterference patterns of a combined grating employed in certainembodiments of inventions disclosed.

[0028]FIG. 7b is an illustration of an additional design for all-opticalswitching of an information carrier-beam between ports using a controlbeam according to certain embodiments of inventions disclosed.

[0029]FIG. 7c are graphs showing all-optical switching of an informationcarrier-beam between the ports using different pulse width and timedelays between the carrier and control beams according to certainembodiments of inventions disclosed.

[0030]FIG. 8a shows another all-optical design for controlling theinterference patterns of a combined grating according to certainembodiments of inventions disclosed.

[0031]FIG. 8b illustrates additional an all-optical switching device forswitching the information carrier beam between ports using the controlbeam according to certain embodiments of inventions disclosed.

[0032]FIG. 9 is an illustration of various alternative design featuresfor a combination transmitting and reflecting grating according tocertain embodiments of inventions disclosed.

[0033]FIG. 10a shows another variation on an optical switching componentproviding greater energy transfer and/or ports according to certainembodiments of inventions disclosed.

[0034]FIG. 10b is an illustration of a retrofit embodiment for a switchcomponent according to certain embodiments of inventions disclosed.

[0035]FIG. 11a shows an all-optical switching and modulating systemusing an interference optical waveguide device according to certainembodiments of inventions disclosed.

[0036]FIG. 11b illustrates an all-optical switching and modulatingsystem using an interference device made of optical waveguides andoutput ports according to certain embodiments of inventions disclosed.

[0037]FIG. 11c is an illustration of an all-optical switching andmodulating system with a self-control feature according to certainembodiments of inventions disclosed.

[0038]FIG. 11d illustrates a different design for an all-opticalswitching and modulating system with control symbology integrated in aninformation beam according to certain embodiments of inventionsdisclosed.

[0039]FIG. 12 shows all-optical switch that is self controlled using apredetermined code.

[0040]FIG. 13 illustrates a symbology usable with an all opticalencoding/decoding system of embodiments of the inventions.

[0041]FIG. 14 illustrates a demultiplexer usable with optical an alloptical encoding/decoding system of embodiments of the inventions.

[0042]FIGS. 15a and 15 b illustrate an ultra-fast all-opticalmodulator/switch and an all-optical multiplexing device made therefrom,respectively, according to embodiments of inventions disclosed.

[0043]FIG. 15c shows an all-optical network system including an alloptical system for multiplexing and demultiplexing connected by along-haul fiber optic channel according to embodiments of inventionsdisclosed.

[0044]FIG. 16A illustrates a mechanism for taking long pulses typicallygenerated by current technology and chopping them to make very narrowpulses using mechanisms in accord with embodiments of the inventionsdisclosed.

[0045]FIG. 16B illustrates a mechanism for encoding a sequence of twosuccessive pulse-symbols to provide a first layer of routing informationso that they can be routed by a switch in accord with embodiments of theinventions disclosed.

[0046]FIG. 16C illustrates a mechanism for encoding a sequence of twosuccessive pulse-symbols to provide a second layer of routinginformation so that they can be routed by a switch in accord withembodiments of the inventions disclosed.

[0047]FIG. 16D illustrates a mechanism for encoding a sequence of twosuccessive pulse-symbols to provide a third layer of routing informationso that they can be routed by a switch in accord with embodiments of theinventions disclosed.

[0048]FIG. 16E is an annotated diagram illustrating an encoding schemefor multilayer switching according to embodiments of inventionsdisclosed.

[0049]FIG. 16F illustrates the effect of each switch layer on symbologyfor routing a data pulse.

[0050]FIG. 17 illustrates a system in which a combination of WDM and aform of symbology provided by an invention disclosed, in which thesymbology is used for CDM.

[0051]FIG. 18 shows some principles involved with directional couplersused for a coincidence devices according to embodiments of inventionsdisclosed.

[0052]FIG. 19 shows some principles involved with Y-couplers used for acoincidence devices according to embodiments of inventions disclosed.

[0053]FIGS. 20 and 21 illustrate basic operation of a component of acoincidence device based on direction couplers according to embodimentsof inventions disclosed.

[0054]FIGS. 22, 23, and 24 illustrate the basic operation of acoincidence gate device in first and second noncoincidence states and acoincidence state, respectively according to embodiments of inventionsdisclosed.

[0055]FIG. 25 illustrates a coincidence gate device that is a variationof the embodiments of FIGS. 22-24 employing a star coupler instead ofmultiple Y-junctions for discussing alternative design concepts.

[0056]FIG. 26 illustrates a coincidence gate device that is a variationof the embodiments of FIGS. 22-24 compatible with waveguideimplementation for discussing alternative design concepts and forillustrating an alternative way of splitting the signals at the inputend of a self-triggering-type coincidence gate.

[0057]FIG. 27 illustrates a coincidence gate device that is a variationof the embodiments of FIGS. 22-24 compatible with waveguideimplementation and using a start splitter instead of directionalcouplers for discussing alternative design concepts.

[0058]FIG. 28 illustrates principles involved with dielectric beamsplitters for purposes of discussing alternative embodiments ofinventions disclosed.

[0059]FIG. 29 illustrates principles involved with metallic beamsplitters for purposes of discussing alternative embodiments ofinventions disclosed.

[0060]FIG. 30 illustrates energy routing in a transmission/reflectiongrating of certain embodiments of inventions disclosed.

[0061]FIGS. 31 and 32 illustrate energy routing in two types ofY-junction used in certain embodiments of inventions disclosed.

[0062]FIG. 33 illustrates energy routing in a grating with a pitch thatis much greater than the wavelength of a light signal and whichfunctions in a manner that is similar to a beam splitter as used incertain embodiments of inventions disclosed.

[0063]FIGS. 34, 35, and 36 illustrate an embodiment of a coincidencedevices consistent with certain embodiments of inventions disclosed andemploying a beam splitter and Y-junction for discussing certain conceptsof these embodiments.

[0064]FIGS. 37, 38, and 39 illustrate an embodiment of a coincidencedevices consistent with certain embodiments of inventions disclosed andemploying a beam splitter and a different kind of Y-junction fordiscussing certain concepts of these embodiments.

[0065]FIGS. 40, 41, and 42 illustrate embodiments based on beam splitterand beam-splitter-like coincidence devices for purposes of discussingvarious embodiments of inventions disclosed.

[0066]FIG. 43 illustrates a conceptual description of a coincidencedevice for abstracting certain concepts involved in various embodimentsof coincidence devices of inventions disclosed in which the interferenceinvolves a first ratio of routed energy in the coincidence andnoncoincidence states.

[0067]FIG. 44 illustrates a conceptual description of a coincidencedevice for abstracting certain concepts involved in various embodimentsof coincidence devices of inventions disclosed in which the interferenceinvolves a second ratio of routed energy in the coincidence andnoncoincidence states.

[0068]FIG. 45 illustrates a conceptual description of a coincidencedevice for abstracting certain concepts involved in various embodimentsof coincidence gates of inventions disclosed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069]FIGS. 1a and 1 b illustrate the optical operational principle ofknown transmitting and reflecting gratings, respectively. FIGS. 1a and 1b may assist in understanding the present invention. FIG. 1a shows atransmitting grating 2 with openings 4 with pitch d. Grating 2 receivesplanar radiation waves 6 on its side 8. Only part of the radiation ofthe impinging waves 6 is transmitted, by openings 4, to the other side10 of grating 2. Beam 12 exits from openings 4 and has a cylindricalwavefront (diffraction effect) and its intensity is distributedisotropically over half cylinders 14 along which it propagates.

[0070] The radiation of propagating fronts 14 (in the shape ofcylinders) interfere with each other to create constructive anddestructive interference. Arrows 16 schematically illustrate thedirections along which the constructive interference exist. Thedirections of arrows 16 are indicated by angles θ, measured in radians,with respect to the axis of symmetry 18 of grating 2. Arrows 16 actuallyindicate the antinodes along which beam 6 is concentrated, due tograting 2, and thus point to the values of intensity peaks at thevarious angles θ, on the coordinate relative to the normal 18. Thelatter is a part of plot 20, which illustrates the spatial distributionof the radiation intensity I of beam 6 versus angle θ. Arrows 16 pointto the angle values θ in which the intensity I of beam 6 reaches localmaxima 22.

[0071] The mathematical relationships between intensity I of beam 6,transmitted by grating 2, and propagation angle θ of this radiation aregiven by equation (1):

I∝[sin (n·β·d·sin (θ)/2)/sin (β·d·sin (θ)/2)]2  Eq. (1)

[0072] In this equation n is the number of openings 4 and β is the wavevector of beam 6 that is equal to 2·π/λ and λ is the wavelength of beam6.

[0073] The intensity I according to Eq. (1) reaches a local maximumvalue when:

(β·d·sin(θ)/2))=i·π  Eq. (2)

[0074] This occurs when I is an integral number, known as the order ofthe diffraction.

[0075] When substituting β for 2·π/λ in Eq. (2), it takes the form:

sin(θ)=i·λ/d  Eq. (3)

[0076]FIG. 1b shows transmitting grating 32 with mask stripes 34arranged with pitch d. Grating 32 receives radiation planar waves 36 onits side 38. Only part of the radiation of waves 36 is reflected back bymask stripes 34 and out from grating 32. Stripes 34 have diffusivereflecting surfaces and are very narrow (diffraction effect). Thus theyreflect the radiation with equal intensity in any direction. Beam 42reflected from stripes 34 have a cylindrical wavefront and its intensityis distributed isotropically over half cylinders 44, defined by thelocus of directions of propagation. The beams from propagating cylinders44 interfere with each other to create constructive and destructiveinterference. Arrows 46 schematically illustrate the directions alongwhich there is constructive interference. The directions of arrows 46are indicated by angles θ, measured in radians, with respect to thenormal 48 of grating 32 surface. Arrows 46 actually indicate theorientations along which beam 36 is concentrated by grating 32. Thevalues of angles θ are indicated on the θ axis. This axis is a part ofgraph 50, which illustrates the spatial distribution of the radiationintensity I of beam 36 versus angle θ. Accordingly it is clear thatarrows 46 point out the angle values θ at which the intensity I of beam36 reaches local maximum values 52.

[0077] The mathematical relationships between intensity I of beam 36,reflected by grating 32, and propagation angle θ of this radiation aregiven by equation (4) below:

I∝[sin (n·β·d·sin (θ)/2)/sin (β·d·sin (θ)/2)]2  Eq. (4)

[0078] In this equation n is the number of stripes 34, d is the spacingbetween lines 34 and β is the wave vector of beam 36 that is equal to2-7/k and λ is the wavelength of beam 36.

[0079] The intensity I according to Eq. (4) reaches a maximum valuewhen:

(β·d·sin(θ)/2))=i·π  Eq. (5)

[0080] This occurs when I is an integral number known as the order ofthe reflection.

[0081] When substituting 2·π/λ for β in Eq. (5) it takes the form:

sin(θ)=i·λ/d  Eq. (6)

[0082] For both types of the gratings, the diffraction(transmitting—FIG. 1a) grating and the reflecting grating (FIG. 1b), themathematical formulas are the same.

[0083] The angles θi in which the intensity of the radiation that comesfrom the gratings is maximal are known as the diffraction orders i ofthe gratings. Accordingly, the angles θi of the transmission andreflecting orders are given by Eq.(7).

sin(θi)=i·λ/d  Eq.(7)

[0084] This occurs when i is an integral number and can get the values+/−0, 1, 2, . . . .

[0085] The incident angle φ of the incoming radiation is measuredrelative to a normal to the grating. When the incident angle φ, of theradiation that hits diffracting and reflecting gratings is off thenormal to the grating, i.e., it differs from an incident angle equal tozero, then Eq.(7) becomes:

sin(θi)+sin(φ)=i·λ/d  Eq. (8)

[0086] This means that the whole pattern of interference is rotated byan angle φ. For a diffracting grating it means that the zero order ofthe grating is located on a line along which the incident radiationpropagates toward the grating. For a reflecting grating it means thatthe zero order of the grating is located on a line that is symmetricwith respect to the normal of the grating. I.e., it forms an angle thatis equal in magnitude on the opposite side of the normal of the gratingsurface.

[0087]FIG. 2a is a side view and schematic illustration according to acombination 100 of transmitting and reflecting gratings formed on acommon surface 102 of transparent block 104 according to embodiments ofinventions disclosed. Block 104 can be made, for example, ofsemiconductors such as Si, GaAr, InGaAr, quartz, glass, silica, fusedsilica or plastic. A block is not essential as may be observed byinspection, but provides a convenient mechanism for manufacture andsupport of the grating. Alternatively a clear planar piece of materialmay be used to support the gratings.

[0088] Combined grating 100 includes two layers of gratings 106 and 108.Grating layer 106, on surface 102, is made of high-absorption materialthat is not transparent and has a surface with a very low reflection.For example, grating layer 106 can be made of silver oxide, which iswidely used in the field of projection masks for photolithography.

[0089] Grating layer 108 is made of a material having a surface with avery high-reflectivity. For example, grating layer 108 can be made ofindium oxide in a similar way to that used to fabricate reflectors andmirrors.

[0090] Grating layers 106 and 108 can be produced by standard techniquesused to produce gratings. For example layer 106 is formed continuouslyover surface 102 and coated by a photoresist material. The photoresistis exposed with Ultra Violet (UV) radiation by known holographictechniques. (Holography involves the interference of two beams having apredetermined angle between them which produce an interference pattern.)Also exposure can be made through a projection mask.

[0091] The photoresist is backed in an oven after its exposure and isdipped (or soaked) in a developer to create openings in the photoresist,above layer 106, in the areas that were exposed. Dipping (or soaking)the photoresist is done in a selective etching acid, such as aceticacid, which does not attack the photo resist and surface 102. Thiscreates, by selective etching, openings 110 in layer 106 through theopenings in the photoresist. After removing the photoresist withacetone, layer 106 on surface 102 of block 104 takes the form of gratinglayer 106 having multiple lines 114 and multiple openings 110.

[0092] For example, the following process, known as lift-off, canproduce grating layer 108:

[0093] 1. Cover grating layer 106 with a layer of photoresist.

[0094] 2. Create centered openings in the photoresist above lines 114 ofgrating 106, by the exposing and developing techniques described above.

[0095] 3. Deposit or evaporate a continuous layer 108 on top of thepatterned photoresist.

[0096] Dip Layer 108 in Acetone Vibrated at an Ultrasonic Frequency(Lift-Off Technique)

[0097] The liftoff technique removes all the areas that were on top ofthe photoresist material and leaves only lines 116 of reflectinggrating-layer 108; these are centered on lines 114 of grating layer 106.

[0098] The formation of grating layer 108 centered on top of gratinglayer 106 completes the fabrication of combined grating 100.

[0099] Lines 118, 120, and 122 of block 104 have cuts 124, 126, and 128,respectively. Cuts 124, 126, and 128 indicate that the drawing of FIG.2a is not scaled. Especially, the dimensions of combined grid 100 arenot scaled. In reality the dimensions of combined grating 100 are verysmall relative to the dimensions of block 104 and they are enlarged inFIG. 2a for clarity.

[0100] For example, the widths S1, S2, and S3 of openings 110, lines114, and lines 116 of grating layers 106 and 108, respectively, are ofthe same order of magnitude as the wavelength λ of the radiation used inoptical communications (about 1.3 μm and 1.51 μm). The total thickness Wof grating layers 106 and 108 together can be less than 0.1 μm and isnegligible with respect to the radiation wavelength λ.

[0101] When planar-wave beam 132 is directed toward combined grating100, part of it passes through openings 110 and is diffractedisotropically with a cylindrical wavefront 133 to create an interferencepattern based upon grating layer 106. The other part of beam 132 isabsorbed by lines 114 and is lost.

[0102] When planar-wave beam 134 is directed toward combined grating100, part of it passes through openings 110 and is lost. Lines 116 ofgrating layer 108 reflect the other part of beam 134.

[0103] Reflecting lines 116 of grating layer 108 may be deposited orevaporated at a high-rate to create a grainy surface, which produces adiffuse-reflecting surface. The diffuse-reflecting surface of lines 116reflects beam 134 isotropically as beam 136 having a cylindricalwavefront to create an interference pattern based upon grating layer108.

[0104] When planar-waves 132 and 134 are applied simultaneously,combined grating 100 acts simultaneously as the combination of gratinglayers 106 and 108. When the beam to be transmitted 132 is in phase withthe beam to be reflected 134 and both have equal intensities, theinterference pattern of combined grating 100 is like gratings 106 or108. However in this case grating 100 has half the pitch (doubleperiodicity or double the density in terms of numbers of lines per unitlength).

[0105] Accordingly, when only beam 132 or 134 is directed towardcombined grating 100, then the grating 100 produces an interferencepattern that is about the same for both situations corresponding to theinterference pattern of gratings 106 or 108, respectively. When bothbeams '132 and 134 are directed toward combined grating 100, thengrating 100 produces an interference pattern that is a combination ofthe interference patterns corresponding to the interference pattern ofgratings 106 and 108. It is equivalent to an interference pattern of agrating having half of the pitch of gratings 106 or 108. The latter isof lower order than either of the former patterns.

[0106] One important condition that is preferably maintained is thephase-matching between beam 133 diffracted from openings 110 of gratinglayer 106 and beam 136 reflected from lines 116 of grating layer 108.This phase-matching preferably should be maintained over and alongsurface 102. Assuming that beams 132 and 134 have the same wavelength λ,then the phase-matching depends on angles φ0, φ1, and φ2. Angles φ0 andφ1 are the impinging incident angles of beams 132 and 134 on combinedgrating 100, respectively, and are measured relative to line 138 that isnormal to grating 100 and surface 102. Angle φ2 is the angle betweenline 140 (parallel to line 122) and surface 102 when line 140 is normalto the direction in which beam 134 propagates.

[0107] Phase-matching along surface 102 is achieved when the followingmathematical condition is fulfilled:

β1·sin(φ1)=β0 sin(φ0)  Eq. (9)

[0108] Here β1=2π·N1/λ and β0=β1=2·N0/λ and N1 is the refractive-indexof the material of block 104. N0 is the refractive-index of the air andis equal to 1. When substituting the expression for β in Eq. (9) andreorganizing its form, Eq. (9) takes the form of the optical law knownas Snell's law:

N 1 ·sin(φ1)=N 0·sin(φ0)  Eq. (10)

[0109] The mathematical relationships between φ0, φ1, and φ2 are:

φ0=90°−φ2 and φ0=φ2  Eq. (11)

[0110] By substituting Eq. (11) in Eq. (10) and reorganizing Eq. (10) weget:

φ2=arc tang(N 1/N 0)=arc tang(N 1)  Eq. (12)

[0111] For example, if N1=1.5 then φ2=56.3°.

[0112]FIG. 2b shows an additional design for a combined transmitting andreflecting grating designed according to embodiments of inventionsdisclosed. This design is similar to that of FIG. 2a and thus the samenumerals are used to indicate similar parts. The design of combinedgrating 100 is achieved by bonding block 105 to block 104 of FIG. 2a.Thus, the parts of the design in FIG. 2b that are similar to those ofFIG. 2a are not explained again here.

[0113] Block 105 may be made of the same material as block 104 and thusmay have the same index of refraction. Block 105 may be bonded to block104 by index-matching glue having the same refractive index as theblocks. Such glue is commonly used in optical components. Such glue doesnot cause any reflection of the radiation that passes between blocks.The absence of such reflection hides surface 102; therefore it isillustrated by a broken line. Avoiding reflection between blocks allowscomplete transmission of beam 132 through openings 110. Because of this,the refractive index on both sides of combined grating 100 is the sameand is equal to N1.

[0114] By substituting index N0 with index N1 in Eqs. (11) &(12) we get:

φ0=φ1=φ2=45°.

[0115]FIG. 3 schematically illustrates the interference pattern ofcombined grating 100. Grating 100 is illustrated according to itsversion shown in FIG. 2a but it can be designed without any limitationaccording to the design shown in FIG. 2b. Beam 132 enters to transparentblock 104 without direction change and impinges on combined grating 100at incident angle φ1 relative to the normal 138 of grating 100. Anglesφ0, φ1, and φ2 are adjusted according to Eqs (11) and (12), with angleφ2 measured relative to line 140. Beam 132 impinges on grating 100 onthe side that includes grating layer 106. Part of the radiation thatpasses through openings 110 is diffracted and interferes to produce aninterference pattern. The interference pattern has three orders in whichconstructive interference exists. These project in the directions of θ0,θ1, and θ−1 indicated by beams 152, 154, and 156, respectively, andcorrespond to the interference indices i=0, 1, and −1.

[0116] Graph 150 illustrates a curve of the intensity I of (shown inrelative units) versus the interference angle θ (measured in radians).The interference orders of graph 150 are indicated by their indices(i=0, 1, and −1). The axis of graph 150, along which interference angleθ is measured, is scaled to mach between angles θ0, θ1, and θ−1, atwhich orders 0, 1, and −1 exist on this axis, and angles θ0, θ1, and θ−1along which beams 152, 154, and 156 propagate, respectively.

[0117] According to Eq. (8) the maximum value that the index of theorders i can get is the value that satisfies the relation:sin(θi)+sin(φ1)=i·λ/d. The maximum absolute value of sin(θi) is 1. Thezero order on axis θ of graph 150 was chosen to be at the origin. Thismeans that for the presentation of graph 150, sin(φ1) is chosen to bezero. Thus i·λ/d should be less than 1 for positive values of i and morethan (−1) for negative values of i. The fact that graph 150 has onlythree orders means, according to Eq. (8), that the index i can only havethe values of 0 and ±1 which means that the absolute value of index isless than 2 (i<2). Accordingly the pitch spacing d of grating layer 106must satisfy d<2%.

[0118]FIG. 4 schematically illustrates the interference pattern ofcombined grating 100 irradiated from two directions. Grating 100 isconsistent with the nomenclature and description provided with referenceto FIG. 2a, but can also be designed, without any limitations, accordingto the design shown in FIG. 2b or others. Beam 132 enters transparentblock 104 without direction change and impinges on combined grating 100at incident angle φ1 relative to line 138 that is normal to grating 100.Angles φ0, φ1, and φ2 are adjusted according to Eqs (11) and (12) formaintaining phase-matching between beams 133 and 136, transmitted andreflected, respectively, by grating 100. Angles φ0, φ1, and φ2 arecalculated by taking into account the value of the refractive index N1of the material of block 104. Angle φ2 is measured relative to line 140.

[0119] Beam 132 impinges on grating 100 on the side with grating layer106. Part of beam 132 is absorbed by lines 114 and is lost. The otherpart of beam 132 passes through openings 110 and is diffracted out fromgrating 100, as beam 133.

[0120] Beam 134 impinges on grating 100 on its other side that includesgrating layer 108. Part of beam 134 passes through openings 110 and islost. The other part of beam 134 is reflected isotropically from lines116 of grating layer 108 of combined grating 100, as beam 136.

[0121] Beams 132 and 134 impinge on grating 100 simultaneously. Lines116 are centered between openings 110 and thus the pitch for bothgrating layers 106 and 108 is the same. Beam 133, diffracted out fromopenings 110, and beam 136, reflected from lines 116, interferes toproduce an interference pattern. The pitch of combined grating 100 isthe space between lines 116 and openings 110 and thus is equal to halfof the pitch of grating layer 106 or grating layer 108. The interferencepattern of grating 100 has one order (zero order) in which constructiveinterference exists in the directions of θ0 indicated by beam 152 andcorresponds to the interference index i=0.

[0122] Graph 150 illustrates a curve of the intensity I of theinterfered radiation (shown in relative units) versus the interferenceangle θ (measured in radians). The interference order of graph 150 isindicated by its index (i=0). The axis of graph 150 along whichinterference angle θ is measured is scaled to match angle θ0 at whichorder 0 exists on this axis, and angle θ0 along which beam 152propagates.

[0123] According to Eq. (8) the maximum value that the index of theorders i can have is the value that still maintainssin(θi)+sin(φ1)=i·λ/d. The maximum absolute value that sin(θi) can haveis 1. The zero order on axis θ of graph 150 was chosen to be at theorigin. This means that for the presentation of graph 150, sin(θ1) ischosen to be zero. Thus i·λ/d should be less than 1 for positives valuesof i and more than (−1) for negative values of i. The fact that graph150 has only one order means, according to Eq. (8), that index i canhave only the values of 0. This means that the absolute value ofindex·i<1. Accordingly the pitch spacing d of combined grating 100 mustsatisfy d<λ and it is half of the pitch d of grating layers 106 or 108,as derived above from Eq. (8) as explained in connection with FIG. 3.

[0124] The above result is in agreement with the pitch relationshipsbetween grating layers 106 and 108 and combined grating 100.

[0125] While grating layers 106 and 108 have pitch d between openings110 or between lines 116, respectively, combined grating 100 has pitchd/2 between openings 110 and lines 116. On the other hand the conditionsfor producing the interference patterns of graph 150 in FIG. 3 (threeorders of interference produced by grating layer 106) and of graph 150in FIG. 4 (one interference order produced by combined grating 100) ared<2λ and d<λ, respectively. These conditions are identical to therelationships between the pitches of grating 106 (or 108) and grating100 in which grating 100 has half of the pitch of grating 106 (or 108).

[0126] Beam 134 is symmetric to beam 132 with respect to grating 100 interms of phase-matching. Grating layers 106 and 108, on both sides ofgrating 100, have the same pitch. Accordingly, it is clear that whenonly beam 134 impinges on grating 100, it will produce an interferencepattern similar to that shown in graph 150 of FIG. 3 created when onlybeam 132 impinges on grating 100.

[0127]FIG. 5 illustrates two graphs 150A and 150B showing two curves ofthe interference intensity I versus the interference angle. Theintensity I is shown in relative units and the angle θ is measured inradians.

[0128] Graph 150B is related to the situation illustrated by graph 150of FIG. 3, which is produced by irradiating combined grating 100 fromone direction, either by beam 132 or by beam 134. The interferencepattern of graph 150B has three orders 0, 1, and −1 at angles θ₀, θ₁,and θ⁻¹, respectively.

[0129] Graph 150A illustrates the situation of FIG. 4, which is producedby irradiating combined grating 100 from two directions andsimultaneously by beams 132 and 134. The interference pattern of graph150A has one zero order at angle θ₀.

[0130] The fact that each of the three interference orders 0, 1, and −1appears at different angles θ₀, θ₁, and θ⁻¹, respectively, allows theseparate collection of the radiation of each order. Accordingly orders0, 1, and −1 of the interference pattern shown in graph 150B can becollected by only three ports P₀, P₁, and P⁻¹, respectively.

[0131] As illustrated in FIG. 6b (discussed in detail below) ports P₀and P⁻¹ can be joined together into one port P₂ in such a way that thebeams they collect and transfer to port P₂ cancel each other under theconditions illustrated in graph 150B. In this configuration, illustratedin graph 150B, the output at port P₂ is zero (the difference between theintensities of order 0 and −1) and the output at port P₁ contains theintensity of order 1.

[0132] For the same configuration and for the situation illustrated ingraph 150A, the output, at port P₀, contains the intensity of order 0that is the only existing order. Order −1 has zero intensity and thusthe difference between the intensities of orders 0 and −1, which appearsin port P₂, equal the intensity of order 0. In this case, the output atport P₁, which equals the intensity of order 1, is equal to zero.

[0133] Accordingly, for the configuration of ports P₀, P₁, P⁻¹, and P₂,described above, the output of port P₂ is zero for the situation shownin graph 150B. This is related to the case when grating 100 isirradiated only from one side, either by beam 132 or by beam 134. On theother hand, for the situation shown by graph 150A, which is related tothe case where combined grating 100 is irradiated simultaneously on bothof its sides by beams 132 and 134, port P₂ contains the intensity of theonly existing order, order 0.

[0134] Similarly, for the configuration of ports P₀, P₁, P⁻¹, and P₂,described above, the output of port P₁ contains the intensity of order 1for the situation shown in graph 150B. this is related to the case whencombined, grating 100 is irradiated simultaneously on both of its sidesby beams 132 and 134. On the other hand, for the situation shown bygraph 150A, related to the case when grating 100 is irradiated only fromone side either by beam 132 or by beam 134, port P₁ contains theintensity of order 1, which is zero.

[0135] Thus we have moved from irradiating grating 100 simultaneously onboth of its sides by beams 132 and 134 to irradiating grating 100 onlyon one of its sides by either beam 132 or beam 134. This move switchesthe radiation intensity from port P₂ to port P₃ and vice-versa.

[0136]FIG. 6a—Controlling Interference Patterns Of Combined Grating

[0137]FIG. 6a illustrates optical system 200, which controlsinterference pattern 150 (not shown) of combined grating 100, bycontrolling different illuminations of beams 132 and 134 on grating 100.Optical fiber 202 guides and emits beam 132 toward lens 204 thatconverts beam 132 to parallel beam 132. Beam 132 is the informationcarrier beam used in optical communication. Reflector 206 receives beam132 and reflects beam 132 toward attenuator 208, which transmits beam132 toward transparent block 104. Beam 132 enters block 104 withoutdirection change and propagates in block 104 toward grating layer 106 ofcombined grating 100.

[0138] Laser 210 is optically coupled to optical fiber 212 and iscontrolled by control unit 214. Fiber 212 guides and emits beam 134,produced by laser 210, toward lens 216 that converts beam 134 intoparallel beam 134. Beams 132 and 134 have the same wavelength λ andlenses 204 and 216 can be, for example, of the type of Graded Index(GRIN) lens commonly used to expand the beams emitted from opticalfibers. Lens 216 direct parallel beam 134 toward reflector 218 thatreflect beam 134 toward grating layer 108 of combined grating 100.

[0139] Incident angles φ1 and φ0 of parallel beams 132 and 134,respectively, and angle φ2 dictate the orientation of combined grating100. These angles are adjusted to maintain phase-matching between beam132, transmitted by grating 100 and beam 134, reflected by grating 100.Attenuator 208 is adjusted to assure that the intensity of beam 132,transmitted by grating 100, is equal to the intensity of beam 134,reflected by grating 100.

[0140] Wen control unit 210 turns off laser 210, beam 134 does notexist. In this case only beam 132 impinges on combined grating 100 onthe side that includes grating layer 106. The latter has a pitch spacingd that satisfies, for example d<2λ. Grating layer 106 of combinedgrating 100 acts as a diffraction grating on beam 132 and producesinterference pattern 150 of three beams corresponding to interferenceorders having indices i=0, 1, and −1. In this case the interferencepattern 150 produced by beam 132 and grating layer 106 of grating 100 issimilar to the interference pattern illustrated by graph 150B of FIG. 5.

[0141] When control unit 214 turns on laser 210, beams 134 and 132 hitthe combined grating 100 on both of its sides, including grating layers106 and 108. Beam 132 impinges on combined grating 100 on its side thatincludes grating layer 106 and beam 134 impinges on combined grating 100on its other side that includes grating layer 108. Reflecting lines 116of grating layer 108 that reflect beam 143 are centered between openings110 of grating layer 106, which transmits beam 132. Thus grating layers106 and 108 have the same pitch d. Thus, combined grating 100 has apitch d that is half the pitch d of gratings 106 and 108. Accordingly,pitch d of combined grating 100 satisfies the relationship d<λ. Combinedgrating 100 acts on beams 132 and 134, impinging on both of its sidessimultaneously, and produces interference pattern 150 of one beamcorresponding to interference order having only the index i=0. In thiscase interference pattern 150 produced by beams 132, 134 and combinedgrating 100 is similar to the interference pattern illustrated by thecurve of graph 150A of FIG. 5.

[0142] Each time control unit 214 turns off control beam 134,interference pattern 150 includes three beams (interference orders 0, 1and −1). In the complementary cases when control unit 214 turns oncontrol beam 134, the interference pattern 150 includes only one beam(interference orders 0) and orders 1 and −1 disappear. In these cases,grating layer 106 and beam 134 produce interference pattern 250, whichhas three beams (interference orders 0, 1, −1), which change theirorientation according to Snell's law while exiting block 104.Interference pattern 250 exists every time that beam 134 is on, evenwhen beam 132 is off.

[0143]FIG. 6b illustrates the optical system 200 of FIG. 6a, describedabove, with receivers or ports P₀, P₁, P⁻¹, and output ports P₂, and P₃arranged to receive and convey energy from the interference pattern 150via a coupling lens 226. When control beam 134 is off, interferencepattern 150 includes three beams. These beams correspond to interferenceorders having the indices i=0, 1, −1 and are optically coupled bycoupling lens 226 into ports P₀, P₁, and P⁻¹, respectively.

[0144] Ports P₀, P₁, and P⁻¹ may be the inputs of optical fibers 230,232, and 234, respectively. Fiber 230, 232, and 234 guide the radiationfrom their inputs to their outputs (ports P₂ and P₃), respectively.Accordingly fiber 234 guides the radiation of interference order −1 toits output P₃. Instead of optical fibers, the ports may be termini ofother types of optical channel mechanism such as a waveguide, lightpipe, mirrors, optical network, etc. depending on the downstreamprocesses to be used. In the current device, further processing isprovided to direct most of the energy toward a signal at port P₂ for anon-interference condition and one at port P₃ for a coincidencecondition.

[0145] Directional coupler 224, whose coupling length 1 is adjusted toproduce a 3 dB directional coupler, couples fibers 230 and 232. Incoupler 224, half of the intensity in fiber 230 is transferred to fiber232 with a phase shift of j where j is a complex number equal to(−1)^(1/2). Similarly, half of the intensity in fiber 232 is transferredto fiber 230 with a phase shift of j that is equivalent to phase shiftof π/2 radians.

[0146] Phase shifter 220 shifts the phase of the radiation in fiber 232by π/2 radians prior to the propagation of the radiation into thecoupling region of directional coupler 224. Accordingly the radiationtransferred from fiber 232 to fiber 230 has a phase shift of π/2+π/2=πradians relative to the radiation that propagates in fiber 230.

[0147] The initial radiation intensities of the beams in ports P₀ and P₁are the same and equal to I. The intensity of the radiation in fiber 230after directional coupler 224 is the sum of half of the initialradiation I in fiber 230 and half of the initial radiation I in fiber232, which has a relative phase difference of 7 radians. Thus the totalradiation intensity in fiber 230 at port P₂ is I/2-I/2=0. This meansthat when control beam 134 is off, the intensity at port P₃ is I and theintensity at port P₂ is zero.

[0148] Alternatively when control beam 134 is on, interference pattern150 includes only one beam corresponding to interference index i=0. Thelatter is coupled, by lens 226, into the input of fiber 230 through portP₀. Interference orders i=1 and −1 disappear and no radiation is coupledby lens 226, into fibers 232 and 234 through ports P₁ and P⁻¹. Thus theintensity at port P₃ is zero. Half of the radiation coupled into fiber230 at port P₀ is lost at directional coupler 224 and the remaining halfpropagates along fiber 230 to port P₂. This means that when beam 134 inon, the intensity at port P₃ is zero and the intensity at port P₂ ishalf of the initial intensity at port P₀. Accordingly, by turningcontrol beam 134 on and off, the intensity of beam 132 can be switchedfrom port P₃ to port P₂, and vice-versa.

[0149] The above description for the switching capability of the systemof FIG. 6b is true for both operation modes of information carrier beam132—the Continuous Wave (CW) mode and the pulse mode.

[0150] Phase shifter 220 can be of the type that applies pressure, byuse of a piezoelectric crystal, on optical fiber 232 to change itsrefractive index and thus to change the phase of the radiation thatpropagates in fiber 232. Phase shifter 220 can be of the type thatthermally changes the refractive index of fiber 232 to change the phaseof the radiation that propagates in this fiber.

[0151] Alternatively, shifter 220 can be made of semiconductor materialfabricated by thin film techniques that change its refractive index dueto injection of charge carriers into its guiding media. This change inthe refractive index shifts the phase of the radiation propagating inthe media of shifter 220. In this case the shifter is a separate deviceand is not an integral part of fiber 232 and thus should have two portsfor coupling fiber 232 into and from device 220. In all the above typesof phase shifter 220, applying voltage to shifter 220 through electrode222 activates shifter 220. Adjustment of the phase shift of shifter 220is achieved by adjusting the applied voltage on electrode 222.

[0152] Phase matching can be obtained by use of a suitable calibrationby closed-loop control. A calibration signal my be passed through theinputs of the devices of any of the foregoing embodiments and the phaseadjusted by means of device such as a phase shifter 220 to provide theproper phase matching. As should be clear from the foregoing discussion,when the phases of the input signals match, the P₂ output, for example,should provide a peak. Due to temperature change, the properties ofvarious optical components may drift, requiring the correction of thephase match. But this correction need only be done at fairly longintervals relative to the rate of data throughput through such devicesand therefore does not present a significant obstacle. Suitable controlsystems for performing calibration are well within the state of the artand can be embodied in many different forms. The subject is thereforenot crucial to the inventions disclosed and is therefore not discussedin greater detail herein.

[0153]FIG. 7a schematically illustrates an optical system 300 that issimilar to optical system 200 of FIG. 6a. System 300 of FIG. 7a differsfrom system 200 of FIG. 6a only in the manner of where the control beam134 comes from. Whereas in system 200 laser 210, controlled by unit 214,produces control beam 134, such control beam 134, in system 300, isproduced by coupling part of the radiation of information-carrier beam132 from optical fiber 202, into optical fiber 304. Directional-coupler302 is a 3 dB directional coupler. Thus coupler 302 couples half of theenergy of carrier beam 132 from fiber 202, in which beam 132 propagates,into fiber 304. The other half of the energy of beam 132 continuespropagating along fiber 202 and is emitted out from port P₄ at theoutput of fiber 202. The radiation energy that is coupled into opticalfiber 304 propagates and guided along this fiber through delay-fiber 306and is emitted, as control beam 134, from fiber 304 at its outputthrough port P₅. Beams 132 and 134 are converted, by lenses 204 and 216,into wide beams 132 and 134, respectively, in the same way that thisconversion is performed in system 200 of FIG. 6a.

[0154] The rest of the optical paths of beams 132 and 134, started fromlenses 204 and 216 in system 300, respectively, are similar to theoptical paths of beams 132 and 134, beginning from lenses 204 and 216 insystem 200, respectively, as illustrated by FIG. 6a. The correspondingdiscussion is therefore omitted here.

[0155] Similarly, interference patterns 150 and 250 are produced, bybeams 132 and 134, in a similar way, in both systems, system 200 andsystem 300 as illustrated in FIGS. 6a and 7 a and explained above in theexplanation of FIG. 6a. Thus the explanations given above for FIG. 6awill not be repeated here.

[0156] Reflector 218 is arranged to move along arrows 308 to gentlyadjust the length of the optical path between reflector 218 and combinedgrating 100 to assure phase-matching between beam 132 passing throughgrating 100 and beam 134 reflected from grating 100. While reflector 218moves along arrows 308 it also causes undesired shifting of the beam 134direction (indicated by arrows 310). To avoid any irradiation change ofgrating 100 by the movement of beam 134 along arrows 310, anon-reflecting, non-transmitting frame with high absorbency may beformed in the surrounding of grating 100. Frame 312 is narrower than thewidth of beam 134 and thus when bean 134 moves along arrows 310, thewhole area of grating 100 remains irradiated.

[0157] Delay-fiber 306 produces a time delay Δt between control beam 134and carrier beam 132. An explanation of how the amount of delay Δtaffects interference patterns 150 and 250 is given below in theexplanations for FIG. 7c.

[0158]FIG. 7b illustrates the same optical system 300 of FIG. 7a,described above, with additional ports P₀, P₁, P⁻¹, P₂, and P₃ arrangedto receive interference pattern 150 from coupling lens 226. Switchingthe emission of the radiation of information carrier-beam 132 betweenports P₂ and P₃ of optical fibers 230 and 234 is achieved by changinginterference pattern 150, having three beams (three interference ordersi=0, 1, and −1) to only one beam (interference order i=0). Theinterference pattern 150 dictates which of ports, P₂ or P₃, is the onethat emits carrier beam 132 in accord with the description attendingFIG. 6b provided above.

[0159] Delay-fiber 306 produces a time delay Δt between what might betermed a control beam 134 and data beam 132. The amount of delay Δtaffects interference patterns 150 and 250 and thus dictates theswitching state between port P₂ and P₃. An explanation of how the amountof delay Δt affects interference patterns 150 and 250 and thus theswitching position between ports P₂ and P₃ is given below in theexplanations for FIG. 7c.

[0160]FIG. 7c shows graphs 356, 358, 360, and 362 of the radiationintensity I versus time t for information-carrier beam 132, control beam134, the radiation emitted from port P₂, and the radiation emitted fromport P₃, respectively. P₂ and P₃ are the ports illustrated by FIGS. 6band 7 b and all the pulses in the above graphs have width T. Intensity Iin graphs 356-362 is shown in arbitrary units and there is no proportionbetween the intensity I of different graphs 356-362.

[0161] Graphs 356-362 are gathered in several groups classifiedaccording to the time delay Δt between information carrier beam 132 andcontrol beam 134. Graph 356-362 of groups 350, 352, and 354 are relatedto time delays Δt=0, Δt<T, and Δt=T, respectively.

[0162] Time-delays Δt between information carrier beam 132 and controlbeam 134 can be produced, for example, by control unit 214 of laser 210as shown in system 200 of FIG. 6b or by delay-fiber 306, as illustratedin system 300 FIG. 7b.

[0163] For graphs 356-362 of group 350, Δt=0, which means that thepulses of information carrier beam 132, shown in graph 356, and thepulses of control beam 134, shown in graph 358, are in phase without anydelay between them. In this case combined grating 100, in opticalsystems 200 and 300 of FIGS. 6b and 7 b, respectively, is irradiated onboth of its sides simultaneously and acts as a grating having pitch d<λ.Accordingly, grating 100 produces interference pattern 150 having onlyone beam (interference order i=0) that is similar to the interferencepattern illustrated by graph 150A of FIG. 5. In such a situation and asexplained above in the description attending FIG. 6b, the radiationintensities of carrier beam 132 and control beam 134 are emitted onlythrough port P₂, as shown by graph 360 resulting in a combined output ofzero, as illustrated by graph 362. Also, it is obvious that when theradiation intensity of both of beams 132 and 134 is zero, then theradiation intensities at ports P₂ and P₃ is also zero, as shown bygraphs 360 and 362, respectively.

[0164] For graphs 356-362 of group 352 Δt<T, which means that the pulsesof information carrier beam 132, shown in graph 356, and the pulses ofcontrol beam 134, shown in graph 358, have a time-overlap T10 betweenthem. Time overlapping T10=T−Δt. In this case, for the time period equalto T10, combined grating 100 in optical systems 200 and 300 of FIGS. 6band 7 b, respectively, is irradiated on both of its sides simultaneouslyand acts as a grating having pitch d<λ. Accordingly, grating 100produces an interference pattern 150 having only one beam (interferenceorder i=0) that is similar to the interference pattern illustrated bygraph 150A of FIG. 5. For the time period of time-overlapping T10, andas explained above with reference to FIG. 6b, the radiation intensitiesof carrier beam 132 and control beam 134 are emitted and together fromport P₂, as shown by graph 360. The radiation intensity in port P₃ iszero, as illustrated by graph 362.

[0165] For the time periods that differ from overlapping interval T10,there are three situations:

[0166] (1) Carrier beam 132 is on and control beam 134 is off. (2)Carrier beam 132 is off and control beam is on. (3) Beams, 132 and 134are off.

[0167] For the first situation, grating 100, of FIGS. 6b and 7 b isirradiated solely, by beam 132, only on the side that includes gratinglayer 106 and thus behaves as a grating having pitch λ<d<2λ. Thisproduces interference pattern 150, which is similar to interferencepattern 150B of FIG. 5. As explained in the description to FIG. 6b,intensity I emitted from port P₂ is zero, as shown by graph 360. Part ofthe radiation intensity of carrier beam 132 is emitted from port P₃ asillustrated by graph 362.

[0168] For the second situation, grating 100 of FIGS. 6b and 7 b isirradiated, solely by beam 134, only on the side that includes gratinglayer 108. Thus it behaves as a grating having pitch λ<d<2λ, whichproduces interference pattern 150 which is similar to interferencepattern 150B of FIG. 5. As explained in the description to FIG. 6b, theintensity I emitted from port P₂ is zero, as shown by graph 360. Part ofthe radiation intensity of carrier beam 134 is emitted from port P₃ asillustrated by graph 362.

[0169] For the third situation, it is obvious that when the radiationintensity of both beams 132 and 134 is zero, in that case, the radiationat ports P₂ and P₃ is also zero as shown by graphs 360 and 362,respectively. For graphs 356-362 of group 354 Δt=T. This means that thepulses of information carrier beam 132, shown in graph 356, and thepulses of control beam 134, shown in graph 358, have a time-overlap ofT10 between them equal to zero. Grating 100 is irradiated alternatelyeither by beam 132 on the side that contains grating layer 106 when beam134 is off or by beam 134 on the side that contains grating layer 108when beam 132 is off. This case is equivalent to switching alternatelybetween the first situation and the second situation described above forgroup 352 of graphs 356-362. The switching between the first and thesecond situations is done immediately. As described above for the firstand the second situations, the intensity emitted from port P₂ is zerofor both of the situations. This is shown by graph 360, and part of theradiation intensities of beam 132 or beam 134 is emitted alternatelyfrom port P₃ in the first or the second situation, respectively.Accordingly, the radiation intensity emitted from port P₂, shown bygraph 360, is always zero and the intensity emitted from port P₃ isalways constant, as shown by graph 362.

[0170] As discussed above, optical systems 200 and 300 of FIGS. 6b and 7b can be operated as optical switches for switching the emittedradiation between ports P₂ and P₃ by changing Δt from zero to Δt=T andvice-versa.

[0171] In addition, optical systems 200 and 300 of FIGS. 6b and 7 b canbe operated as optical modulators for producing very narrow pulses. Forexample, the width of the pulses emitted from port P₂, illustrated bygraph 360 of group 352 is T10 when T10=T−Δt. The pulse width T ofcarrier beam 132 or control beam 134 is the shortest that can beachieved with the technologies known today. When using Δt≈T, then widthT10 of the pulses emitted from port P₂ of systems 200 and 300 of FIGS.6b and 7 b, respectively, approaches zero; This means that the pulses atport P₂ are much shorter than the shortest pulses than can be achievedwith present technologies. The frequency of the short radiation pulsesat port P₂ is equals to the frequency of the original longer pulses ofbeams 132 or 134.

[0172] Optical systems 200 and 300 of FIGS. 6b and 7 b, respectively,can be operated as optical modulators that act like opticaldifferentiator systems. When optical systems 200 and 300 operate as adifferentiator, their operation is similar to electrical differentiatorcircuits in the sense that in both types of differentiators, optical andthe electrical, the short pulses are derived from wider pulses whilemaintaining the original frequency.

[0173] Interference pattern 250 of FIGS. 6a-7 b is produced when controlbeam 134 passes through grating layer 106 when its pitch d satisfiesλ<d<2λ. Accordingly interference pattern 250 includes three beamscorresponding to interference pattern orders i=0, 1, and −1. The beamsof interference pattern 250 exist only when control beam 134 is on andthus they are illustrated in FIGS. 6a-7 b, by broken lines, having theinterference indices i=0, 1, and −1. Similarly, the beams ofinterference pattern 150 have indices of interference orders i=1 andi=−1. They exist only when one of beams 132 or 134 is on and the otherbeam (134 or 132, respectively) is off and thus are also illustrated inFIGS. 6a-7 b by broken lines. Thus, arbitrarily narrow pulses may beformed by feeding suitably-timed pulses into the inputs of the foregoingdevices.

[0174]FIG. 8a schematically illustrates an optical system 400 that issimilar to optical systems 200 and 300 of FIGS. 6a and 7 a,respectively. System 400 of FIG. 8a is differing from systems 200 and300 of FIGS. 6a and 7 a, respectively, only in the way that control beam134 is produced. In system 200, laser 210 is controlled by control unit214 to produce control beam 134. Beam 134 in system 300 is produced by acoupling part of the radiation of information-carrier beam 132 fromoptical fiber 202 into optical fiber 304. The radiation that is coupledinto optical fiber 304 propagates and is guided along this fiber throughdelay-fiber 306 and is emitted, as control beam 134, from fiber 304 atits output through port Ps.

[0175] In optical system 400 of FIG. 8a beam 132 emitted from the outputof optical fiber 202 at port P₄ is converted, by lens 204, into widebeam 132. Beam 132 propagates from lens 204 toward beam-splitter 406.Part of beam 132 is directed toward attenuator 208 and passes throughthis attenuator. Beam 132 continues to propagate from attenuator 208 andenters block 104 to impinge on combined grating 100 on its side thatincludes grating layer 106. The other part of beam 132 is transmitted bybeam-splitter 406 as wide control beam 134 directed toward reflector402. Reflector 402 receives control beam 134 and reflects this beamtoward reflector 216 that reflects and directs beam 134 toward combinedgrating 100. Control beam 134 impinges on grating 100 on its side thatincludes grating layer 108. The rest of the optical paths of beams 132and 134, starting from combined grating 100 in system 400 of FIG. 8a,are similar to the optical paths of beams 132 and 134, starting fromgrating 100 in systems 200 and 300, as illustrated in FIGS. 6a and 7 aand described with reference thereto.

[0176] Interference patterns 150 and 250 are produced by beams 132 and134, in a similar way, in all of the systems, systems 200, 300 and 400as illustrated in FIGS. 6a, 7 a and 8 a and explained above in theaccompanied explanation to FIGS. 6a and 7 a. Thus the explanations givenabove for similar features are not be repeated here.

[0177] Reflectors 402 and 216 may be connected at a point 408, and maybe oriented at a right angle to each other to form a retro-reflector410. Reflector 410 is arranged to move, along arrows 404, to adjustgently the length of the optical path between reflector 216 and combinedgrating 100 to provide phase-matching between beam 132, passing throughgrating 100, and beam 134 reflected from grating 100. The adjustment maybe made automatically or manually. In a functioning system, as discussedabove, a calibration process may be periodically followed to insure thephase matching is optimal and consistent. Note that in addition toregular calibration, adjustment may be made based on peak signaldetected using normal data throughput so that the system is continuouslyadjusted. Alternatively, an error condition may invoke a calibrationprocess. The error condition may be determined based on average energyor peak energy of an output (e.g., from P₃)

[0178] Intensity equalization of the radiation intensities of beam 132,which passes through grating 100, and beam 143, which is reflected fromgrating 100, may be achieved by adjusting the attenuation factor ofattenuator 208.

[0179] While retro-reflector 410 moves along arrows 404 it does notcause any undesired lateral shifting of beam 134 as occurs in system300, in which moving reflector 218 along arrows 308 causes movement ofbeam 134 along arrows 310.

[0180] Large movements of retro-reflector 410 along any desireddistance, oriented in the direction of arrows 404, changes the length ofthe optical path between reflector 410 and grating 100 and thus producesa time delay Δt between control beam 134 and carrier beam 132. Anexplanation of how the amount of delay Δt affects interference patterns150 and 250 is given above with reference to FIG. 7c.

[0181]FIG. 8b illustrates same optical system 400 of FIG. 8a, describedabove, with additional ports P₀, P₁, P⁻¹, P₂, and P₃ arranged to receiveinterference pattern 150 from coupling lens 226. Switching the emissionof the radiation of information carrier-beam 132 between ports P₂ and P₃of optical fibers 230 and 234 is achieved by changing interferencepattern 150 from three beams (three interference orders i=0, 1, and −1)to only one beam (interference orders i=0). The way in which the changeof interference pattern 150 dictates which of ports, P₂ and P₃, is theone that emits carrier beam 132 is similar to the way that isillustrated by FIGS. 6b and 7 b and the attending discussion.

[0182] Retro reflector 410 produces a time delay Δt between control beam134 and carrier beam 132. The length of the delay Δt affectsinterference patterns 150 and 250 and thus dictates the switching stateand therefore whether the output is from port P₂ or P₃ (or neither). Anexplanation of how the delay Δt affects interference patterns 150 and250 and thus the switching between ports P₂ and P₃ is given above in thedescription of FIG. 7c and elsewhere.

[0183]FIG. 9 is another alternative design for a combination of atransmitting and reflecting grating 500 designed according to theinvention. The design is achieved by bonding block 105 to block 104.Blocks 105 and 104 and their glue may have the same index of refraction,as explained above. Avoiding reflection of the radiation passes fromblock 104 to 105 (and vice-versa) allows a complete transmitting ofbeams 132 and 134 through openings 110. Lines 118, 122, and 123 havebreaks 128, 124, and 506 to indicate that the dimensions of combinedgrating 500 and are not proportional to the dimensions of blocks 104 and105. In reality the dimensions of grating 500 may be much smaller thansuggested by the illustration of FIG. 9.

[0184] When blocks 104 and 105 have the same refractive index and arebonded with index matching glue, the refractive index on both sides ofcombined grating 100 is the same and equal to N1. Accordingly, bysubstituting refractive index N0 with refractive index N1 in Eqs. (11)and (12) we get the condition for maintaining phase-matching betweenbeams 132 and 134 all over the planes of grating 500:

φ0=φ1=φ2=45°.

[0185] The same holographic and photolithographic techniques thatproduce combined grating 100 produce also combined grating 500. Grating500 contains grating layers 502, 106, and 108. Reflecting lines 504 and116 of grating layers 502 and 108 are centered along lines 114 ofgrating layer 106.

[0186] The above condition for angles φ0, φ1, and φ2 assures that therewill be phase-matching between the radiation reflected from grating 500and the radiation that passes through grating 500. This phase-matchingis maintained all over both sides of combined grating 500 that includesgrating layers 502 and 108.

[0187] Beam 132 passes through openings 110 of grating layer 106 ofcombined grating 500 and is reflected from mask stripes 504 of gratinglayer 502 of combined grating 500. Similarly, beam 134 passes throughopenings 110 of grating layer 106 of combined grating 500 and isreflected from lines 116 of grating layer 108 of combined grating 500.

[0188] When only beam 132 is incident, part of it passes through gratinglayer 106 of combined grating 500 to produce an interference patternsimilar to interference pattern 150 of FIGS. 6a-8 b. The other part ofbeam 132 is reflected by grating layer 502 of combined grating 500 toproduce an interference pattern similar to interference pattern 250 ofFIGS. 6a-8 b. When only beam 134 is incident, part of it passes throughgrating layer 106 of combined grating 500 to produce an interferencepattern similar to interference pattern 250 of FIGS. 6a-8 b. The otherpart of beam 134 is reflected by grating layer 108 of combined grating500 to produce an interference pattern similar to interference pattern150 of FIGS. 6a-8 b.

[0189] Grating layers 502, 106, and 108 all have pitch d that satisfiesλ<d<2λ. Accordingly, when only one beam 132 or 134 is incident and theother beam (134 or 132, respectively) is not, the resulting interferencepatterns, such as 150 and 250 shown in FIGS. 6a-8 b, and pattern 150Bshown in FIG. 5 result. Interference Pattern 150B has three exitinglobes corresponding to interference orders i=0, 1, and −1.

[0190] When both beams 132 and 134 are simultaneously incident, the partof the radiation of beam 134 reflected from grating layer 108 and thepart of the radiation of beam 132 that passes through grating layer 106produce an interference pattern, such as interference 150 of FIGS. 6a-8b. The combination of grating layers 106 and 108 of grating 500 producesgrating with a pitch d that satisfies d<λ. Accordingly, in this case,the interference pattern is similar to interference pattern 150A of FIG.5 that has only one lobe corresponding to interference order i=0.

[0191] Similarly, when both beams 132 and 134 are incidentsimultaneously, the part of the radiation of beam 132 reflected fromgrating layer 502 and the part of the radiation of beam 134 that passesthrough grating layer 106 produce an interference pattern such asinterference 250 of FIGS. 6a-8 b. The combination of grating layers 106and 502 of grating 500 produces grating with a pitch d that satisfiesd<%. Accordingly, the interference pattern is similar to interferencepattern 150A of FIG. 5 that has only one lobe corresponding tointerference order i=0.

[0192] Combined grating 500 is symmetric with respect to beams 132 and134 and, unlike combined grating 100, it produces interference patternssuch as 150 and 250 of FIGS. 6a-8 b that are the same for anycombination of on-and-off of beams 132 and 134.

[0193] In FIGS. 6a-8 b, when using combined grating 100, only the energyof interference pattern 150 is used, for switching and modulatingpurposes, and the energy of interference pattern 250 is lost. The use ofcombined grating 500 allows using two interference patterns, such asinterference patterns 150 and 250 in FIGS. 6a-8 b, for the same orsimilar applications as shown in FIGS. 10-12 described below.

[0194] For clarity and without limitation, combined grating 500 isillustrated in a simple version that does not include transparent block105. The two versions of grating 500 are analogous to the two versionsof grating 100 in FIGS. 2a and 2 b, without or with transparent block105, respectively.

[0195]FIG. 10a schematically illustrates an all optical modulating andswitching system 600 that is similar to optical system 300 of FIG. 7bwith the following differences. Combined grating 100 in system 300 ofFIG. 7b is replaced in system 600 of FIG. 10a by the more efficientcombined grating 500 illustrated by FIG. 9. Radiation guides 610, 612and 624 collect the radiation of interference pattern 250, in system 600of FIG. 10a. Unlike system 300 of FIG. 7b, in which the radiation ofinterference pattern 250 is lost, system 600 collects the radiation ofinterference pattern 250 to be used in a manner similar to the way thatthe radiation of interference pattern 150 is used. Except for thesedifferences, the components of system 600, their arrangement, and theirmeans of operation are similar to those of system 300 of FIG. 7b. Thusthe explanation for the similar parts of systems 300 and 600 is notrepeated.

[0196] As explained, grating 500 of FIG. 9 produces, with beams 132 and134, interference patterns 150 and 250 that are the same and can be usedfor similar applications. For that reason, unlike system 300, in whichinterference pattern 250 is lost, in system 600 energy in interferencepattern 250 is collected by optical fibers 610, 612, and 624. Fibers610, 612, and 624 have corresponding ports P₁₀, P₁₁, and P⁻¹¹ at theirinputs to collect the beams related to interference orders i=0, 1, and−1, respectively. The radiation of interference pattern 250 propagatingfrom grating 500 is received by coupling lens 626 that couples thisradiation into ports P₁₀, P₁₁, and P⁻¹¹.

[0197] Optical fibers 610, 612, and 624, with their input ports P₀, P₁,and P⁻¹¹ and output ports P₁₂ and P₁₃, are used to collect the radiationof interference pattern 250. These ports are similar to optical fibers230, 232, and 234 with their input ports P₀, P₁, and P⁻¹ and outputports P₂ and P₃ used to collect the radiation of interference pattern150 of FIGS. 6b, 7 b, and 8 b.

[0198] Similarly, directional coupler 614 and phase-shifter 620 with itselectrode 622 are similar to directional coupler 224 and phase-shifter220 with its electrode 222, as illustrated in FIGS. 6b, 7 b, and 8 b.All the components of FIG. 7c are described above for the all-opticalswitching and modulating behavior of ports P₂ and P₃ including thebehavior that depends upon the time delay Δt. Pulse width T also appliesto ports P₁₂ and P₁₃.

[0199] The beams which have the interference orders i=±1 in bothinterference patterns 150 and 250 are indicated by broken lines toillustrate that these lobes disappear when both beams 132 and 134incident simultaneously.

[0200]FIG. 10b illustrates an upgrading unit 700 designed to collect theradiation energy of interference pattern 250 of systems 200 and 400 ofFIGS. 6b and 8 b, when their grating 100 is replaced by grating 500. Asexplained above for grating 500 of FIG. 9, this grating produces, withbeams 132 and 134 interference patterns 150 and 250 that are the sameand can be used for similar applications. In systems 200 and 400 ofFIGS. 6b and 8 b, respectively, the energy in interference pattern 250was lost. However when these systems are integrated with unit 700, theenergy in interference pattern 250 is not lost and is collected byoptical fibers 610, 612, and 624 of unit 700. Fibers 610, 612, and 624have corresponding ports P₁₀, P₁₁, and P⁻¹¹ at their inputs to collectthe beams corresponding to interference orders i=0, 1, and −1,respectively. The radiation of interference pattern 250 propagating fromgrating 500 is received by coupling lens 626, which couples thisradiation into ports P₁₀, P₁₁, and P⁻¹¹.

[0201] Optical fibers 610, 612, and 624 of unit 700, with their inputports P₁₀, P₁₁, and P⁻¹¹ and output ports P₁₂ and P₁₃, are used tocollect the radiation of interference pattern 250. These fibers aresimilar to optical fibers 230, 232, and 234 of systems 200 and 400, withtheir input ports P₀, P₁, and P⁻¹ and output ports P₂ and P₃. Thesefibers are used to collect the radiation of interference pattern 150.

[0202] Similarly, directional coupler 614 and phase-shifter 620 of unit700, with its electrode 622, are similar to directional coupler 224 andphase-shifter 220 of systems 200 and 400, with their electrode 222, asillustrated in FIGS. 6b, 7 b, and 8 b.

[0203] Graphs 360 and 362 of FIG. 7c illustrate the all-opticalswitching and modulating behavior of ports P₁ and P₂ of systems 200 and400, including how this behavior is dependent upon time delay Δt andpulse width T. The illustration of FIG. 7c represents also ports P₁₂ andP₁₃ of unit 700.

[0204] The lobes of interference orders i+1 in interference pattern 250are illustrated by broken lines to show that these beams disappear whenbeams 132 and 134 are simultaneously incident. The resulting lobes arecoupled into ports P₁₁, and P⁻¹¹ by coupling lens 626.

[0205]FIG. 10a already illustrates the integration of unit 700 withsystem 300 of FIG. 7b to produce system 600. The way unit 700 improvesthe efficiency of optical system 600 is described above in theexplanation of FIG. 10a. The improvement of systems 200 and 400 of FIGS.6b and 8 b, by integrating unit 700, is achieved in a similar manner asthat illustrated in FIG. 10a and described above and thus is notrepeated here.

[0206]FIG. 11a schematically Illustrates an optical system 800 for anall-optical switching and modulating system, including interferencedevice 801 made of groups of radiation guides 814 and 816. Informationcarrier beam 132 is optically coupled into ports P₄ at the inputs ofradiation guides 802 of bundle 804. The other sides 810, at the outputsof optical fibers 802, are optically coupled to inputs 813 of waveguides814. Waveguides 814 are one group out of two groups of waveguides 814and 816 that form interference device 801.

[0207] Similarly, control beam 134 is optically coupled into ports P₅ atthe inputs of radiation guides 806 of bundle 808. The other sides 812,at the outputs of optical fibers 806, are optically coupled to inputs815 of waveguides 816. Waveguides 816 are one group out of two groups ofwaveguides that forms interference device 801.

[0208] Waveguides 814 and 816 are interleaved such that one waveguide816 is located in each space between two waveguides 814 and vice-versa.The dimensions of optical fibers 802 and 806 are relatively large; thusthe spaces between waveguides 814 and 816 fit the dimensions of fibers802 and 806. The outputs of fibers 802 and 806 at their ends 810 and 812are also relatively large. Thus inputs 813 and 815 of waveguides 814 and816, respectively, are also designed to be large to allow efficientoptical coupling between fibers 802 and 806 and inputs 813 and 815 ofwaveguides 814 and 816, respectively.

[0209] Waveguides 814 and 816 at output 823 of device 801 are preferablyarranged in a very dense structure to assure that pitch d1 between twofollowing waveguides 814 or 816 satisfies λ<d1<2λ. Also the pitch d2between the two following waveguides 814 and 816 should satisfy d2<λ.

[0210] Note that the configuration of waveguides 814 and 816 changesfrom large waveguides separated by large spaces, at input 817 of device801, to small waveguides separated by small spaces at output 823 ofdevice 801. This is achieved by bending waveguides 814 and 816 andchanging their size by shaping them in a form of an adiabatic taper.

[0211] Device 801 can be made, for example, of silica, fused silica,diffused glass, lithium niobate, liquid crystals, and semiconductorssuch as silicon, GaAs, AlGaAs, InP, InGaAsP, CdTe and CdZnTe. Device 801is made of substrate 820, which carries confinement layer 818 to guidethe radiation. Layer 818 may have an index of refraction that is higherthan the index of refraction of substrate 820. Growing epitaxial layersusing techniques of Liquid Phase Epitaxy (LPE), Molecular OrganicChemical Vapor Deposition (MOCVD), and Molecular Beam Epitaxy (MBE) canproduce layer 818. Diffusing dopants into substrate 820 can also producelayer 818. For example, diffusion of Ag ions into lithium-niobatesubstrate 820 can produce layer 818.

[0212] The fabrication of radiation waveguides 814 and 816 in layer 818of device 801 may be accomplished using standard IC industry etching andphotolithography techniques.

[0213] The radiation of information carrier beam 132 is coupled intoports P₄ of fibers 802 of bundle 804 and exits from fibers 802 at theirends 810. This radiation is then coupled into inputs 813 of waveguides814 at input 817 of device 801. Waveguides 814 carry the radiation ofbeam 132 to the output of guides 814 at output 823 of device 801. Toavoid any delay between the radiation from guides 814 at output 823 ofdevice 801, the total length of all the optical paths between ports P₄and the outputs of guides 814 at output 823 are adjusted to be the same.Alternatively, any differences resulting in phase mismatching may becorrected using adjustable phase correction devices as discussed aboveand below. Phase-matching between the beams from guides 814 at output823 can be achieved by strong coupling between guides 814 to produce aneffect similar to phase lock. To produce more positive phase matchbetween the beams of guides 814, phase shifters 822 can be produced ontop of guides 814 by thin film techniques. The electrodes 824 and 826can control each of phase shifters 822 separately. Controlling phaseshifters 822 is done by applying control voltages to their electrodes824 and 826, which in turn changes the refractive index of guides 814and thus causes a phase shift of the radiation that they guide.

[0214] Maintaining equal intensity of all the beams that exit fromguides 814 at output 823 can be achieved by ensuring equal losses forall the optical paths between ports P₄ and the output of guides 814 atoutput 823. Alternatively, optical amplifiers 828 can be produced, ontop of guides 814, by thin-film techniques. Amplifiers 828 arecontrolled separately through their electrodes 830 and 832 by applyingcontrol voltages. Thus the intensities of the beams in guides 814 atoutput 823 can be controlled to be the same, by adjusting theamplifications of amplifiers 828.

[0215] The radiation of control beam 134 is coupled into ports P₅ offibers 806 to be emitted from guides 816 at output 823 of device 801.This is done analogously to the way in which the radiation ofinformation carrier beam 132 is coupled into ports P₄ to be emitted fromguides 814 at output 823 of device 801. In addition, the same controlfor the phases, the time delays, and the intensities described above forinformation carrier beam 132 propagating in guides 814 is applied tocontrol beam 134 propagating in guides 816.

[0216] Accordingly when the radiation of information carrier beam 132 iscoupled through ports P₄ of bundle 804 of fibers 802, it is divided andexits with the same intensity and phase. It does so from multiple guides814 arranged in every other guide in the combined group of guides 814and 816 at output 823 of device 801.

[0217] Similarly, when the radiation of control beam 134 is coupledthrough ports P₅ of bundle 808 of fibers 806, it is divided and exits.It does so with the same intensity and phase, from multiple guides 816arranged in every other guide in the combined group of guides 814 and816 at output 823 of device 801. The phases and the intensities of beams132 and 134 at the outputs of guides 814 and 816 are equal.

[0218] As indicated above, waveguides 814 and 816 at output 823 ofdevice 801 are arranged in a very dense structure to ensure that pitchd1 between two successive waveguides 814 or 816 satisfies λ<d1<2λ. Alsothe spacing d2 between two following waveguides 814 and 816 shouldsatisfy d2<λ.

[0219] The group of waveguides 814 and 816 at output 823 of device 801is actually a an array of radiation waveguides that act similarly tocombined grating 100, illustrated and explained above. Thus device 801acts as interference device similar to combined gratings 100 and 500.When only information carrier beam 132 or only control beam 134 is on,the combined group of guides at output 823 has a spacing d1 thatsatisfies λ<d1<2λ.

[0220] This means that when only information carrier beam 132 or onlycontrol beam 134 is on, device 801 produces interference pattern 150similar to interference pattern 150B of FIG. 5. The latter is producedby grating 100, and has three lobes corresponding to interference ordersi=0, 1, and −1. When beams 132 and 134 are simultaneously on, thecombined group of waveguides at output 823 has pitch d2 that satisfiesd2<λ. In this case interference pattern 150 that device 801 produces issimilar to interference pattern 150A of FIG. 5, produced by grating 100,and having only one beam corresponding to interference order i=0.

[0221] Interference pattern 150 of FIG. 11a is collected by couplinglens 226 to couple the lobes of this pattern into the ports of anoptical unit (not shown). This unit is similar to unit 700 of FIG. 10bbut does not include grating 500 and coupling lens 626. The latterconverts device 801 into all-optical switch and modulator.

[0222]FIG. 11b illustrates an optical system 900 for all-opticalswitching and modulating. System 900 is a combination of systems 800 ofFIG. 11a and 700 of FIG. 10b. System 700 does not contain grating 500 orcoupling lens 626; the latter is replaced by coupling lens 226 of system800. System 900 produces interference pattern 150 of the types 150A or150B of FIG. 5 according to the on or off condition of beams 132 and134, as illustrated in FIG. 11a and explained above. The operationalprinciple of system 700 is illustrated in FIGS. 6b, 7 b, 8 b, 10 a and10 b and is explained in the attending discussion. System 700 receivesthe radiation of interference pattern 150 and emits this radiationalternatively from ports P₁₂ and P₁₃. When only beam 132 or only beam134 is on, then interference pattern 150 is of the type 150B,illustrated by FIG. 5, and only port P₁₃ emits the radiation ofinterference pattern 150. The latter is coupled to system 700 by lens226 into ports P₁₀, P₁₁, and P⁻¹. The radiation intensity at port P₁₂ iszero.

[0223] Alternatively, when beams 132 and 134 are on simultaneously, theninterference pattern 150 is of the type 150A, illustrated by FIG. 5.Only port P₁₂ emits the radiation of interference pattern 150; thelatter is coupled to system 700 by lens 226 into ports P₁₀, P₁₁, andP⁻¹¹. Here the radiation intensity at port P₁₃ is zero.

[0224] The switching and modulating properties of system 900 areanalogous to those in FIG. 7b. Accordingly, the switching and modulatingbehavior of system 900 is a function of the pulse width T of beams 132and 134 and the delay time Δt between these beams. This is illustratedby FIG. 7c. Control beam 134 can be produced, as shown in FIG. 6b, bylaser 210 that is controlled by control unit 214. When laser 210 isturned on it is impossible to predict the phase of the its beam 134.Accordingly, this configuration has the disadvantage of the difficultyof controlling the phase of beam 134 relative to beam 132. Theconfigurations of FIGS. 11c and 11 d solve this problem.

[0225]FIG. 11c schematically illustrates optical system 100; anall-optical switching and modeling system that is self-controlled.System 1000 includes system 800 of FIG. 11a with an additionalillustration showing how information carrier beam 132 and control beam134 are produced. Information carrier beam 1002 is coupled into opticalfiber 1004 through its input 1001 and propagates inside fiber 1004toward Y-junction 1005. In Y-junction 1005, the radiation of beam 1002is divided into information carrier beam 132 and control beam 134, whichpropagates inside optical fibers 1006 and 1010, respectively. Beam 132exits from fiber 1006 at its output 1008. Beam 132 is collected andexpanded, by coupling lens 1022. It is coupled into ports P₄ of fibers802. Beam 134 propagates inside fiber 1010 through time-delayer 1012 andphase shifter 1014 and exits from fiber 1010 at its output 1018. Beam134 is collected and expanded, by coupling lens 1020. It is then coupledinto port P₅ of fibers 806.

[0226] Time delayer 1012 produces a time delay Δt between beam 132 and134. Phase shifter 1014 changes the phase of beam 134 to match the phaseof beam 132. The delay time Δt, which time delay 1012 produces, dependsupon the extra length of its fiber loop. The voltage applied to controlelectrode 1016 of phase shifter 1014 controls the phase shift of beam134.

[0227] The operational principle of shifter 1014 is similar to that ofshifter 220 of FIG. 6b. The optical paths of beams 132 and 134 fromports P₄ and P₅, respectively, are similar to system 800 of FIG. 11a.Since beams 132 and 134 are both derived from a single beam 1002, phaseshifter 1014 can maintain stable phase-matching between these beams.

[0228]FIG. 11d schematically illustrates optical system 1100 for anall-optical switching and modeling system that is self-controlled.System 1100 includes system 800 of FIG. 11a with an additionalillustration showing how information carrier beam 132 and control beam134 are produced.

[0229] Beam splitter 1104 divides wide information carrier beam 1102into information carrier beam 132 and control beam 134. Beam 132 isreflected by splitter 1104 and is directed toward bundle 804 of fibers802 to be coupled into ports P₄ of fibers 802. Beam 134 propagatesthrough splitter 1104 toward retro-reflector 1106. Retro-reflector 1106receives beam 134, from beam splitter 1104, and reflects beam 134 in theopposite direction with a vertical displacement toward reflector 1108.Reflector 1108 receives beam 134, from retro-reflector 1106, andreflects beam 134 toward bundle 808 of fibers 806. It is then coupledinto port P₅ of fibers 806.

[0230] Retro reflector 1106 is arranged to move along arrows 1110 tochange the length of the optical path of control beam 134 betweensplitter 1104 and port P₅. Accordingly, the movement of retro-reflector1106 along arrows 1110 is used to control both the phase and the timedelay Δt between beams 132 and 134. While a gentle movement of reflector1106 along arrows 1110 controls the phase-matching between beams 132 and134, a large movement of reflector 1106 along arrows 1110 controls thedelay time Δt between beams 132 and 134. The above movements ofreflector 1106 along arrows 1110 maintain the orientation and theposition in which beam 134 hits reflector 1108 and thus do not changethe coupling of beam 134 into ports P₅.

[0231] The optical paths of beams 132 and 134 from ports P₄ and P₅,respectively, are similar to what is illustrated by system 800 of FIG.11a and described with reference thereto. Since beams 132 and 134 areboth derived from a single beam 1102, retro-reflector 1106 can maintainphase-matching between them that is stable.

[0232]FIG. 12 illustrates a modulator and switch 1200 representing anall-optical self-controlled switch that is activated by a predeterminedlogical code of digital pulses representing data in carrier beam 1210.Switch 1200 (alternatively referred to as modulator 1200) represents anyof the optical switches illustrated and described before. For example,switch 1200 includes and represent system 300 of FIG. 7b when input 1202of switch 1200 couples optical fibers 1206 with fibers 202 of system300. Output 1204 of switch 1200 couples port P₂ of system 300 with fiber1208. Switch 1200 may be characterized by the parameters T and Δt “(T,Δt)” in the drawing, where Δt is the time delay produced by time delayer306 of FIG. 7b. The parameter T is the width of the pulses that switch1200 receives at its input 1202 and T1 is the width of the pulses thatswitch 1200 produces at its output 1204.

[0233] Information carrier beam 1210 propagates in core 1214 of fibers1206 and is coupled by input 1202 of switch 1200 to fibers 202 of system300 of FIG. 7b. Beam 1210 is divided, by system 300, into two beams,information carrier beam 132 and control beam 134. Beams 132 and 134inside switch 1200 are phase matched and beam 134 is delayed by Δt withrespect to beam 132. Port P₂ of system 300 is coupled to fiber 1208 byoutput 1204 of switch 1200 to emit pulses from output 1216 of fiber1208. Port P₂ of system 300 produces pulses only when the pulses ofbeams 132 and 134 exist together. The pulse width T received by switch1200 is maintained at output 1216 of fiber 1216 to be equal to T1 onlywhen there is a complete time overlap between the pulses of beams 132and 134.

[0234] Graphs 1230 at the lower part of FIG. 12 show the pulse intensityI versus time t. The scale of the intensity I is arbitrary. Graph 1218is related to the data stream of information carrier beam 1210 and beam132 of system 300. Graphs 1220 and 1222 are related to the data streamof control beam 134 of system 300 and beam 1212 at output 1216,respectively.

[0235] The data stream of beam 1210, illustrated by graph 1218, includestwo pairs of pulses. In each pair the pulses have a width T and areseparated by a time Δt. The pairs of pulses in graph 1218 are separatedby a guard interval T2. The intervals T2, Δt, and T satisfy theinequality, T2>Δt>T. The data stream of beam 132 of system 300 issimilar to the data stream of beam 1210; thus graph 1218 illustrates thedata stream of beam 132 as well.

[0236] Graph 1220 illustrates the data stream of beam 134 of system 300.This data stream 134 is delayed by an amount Δt with respect to the datastream of beam 132 shown in graph 1218. Accordingly the first pulse ineach pair of pulses of beam 134 has a time overlap with the second pulsein each pair of pulses of beam in the input stream 132. Graph 1222illustrates the data stream of beam 1212 at output 1216 of fiber 1208.The pulses of beam 1212 shown in graph 1222 are present only when thepulses of beams 132 and 134, shown in graphs 1218 and 1220,respectively, exist simultaneously.

[0237] Accordingly switch 1200 is a self-activated all-optical switch.Information carrier beam 1210 arranged to include information pulses,each of which is followed by activating pulse at a time space Δt. Theinformation pulses, together with their respective (following)activating pulses defines a pair of pulses each of which may represent asymbol (e.g., a bit) and each of which is separated by time T2>Δt>T.Note that each symbol or pulse pair may, encode more than a single bit,for example by means of pulse amplitude modulation (PAM) or may bephase-encoded as well to provide phase-shift keying (PKM) or quadratureamplitude modulation (QAM) symbols.

[0238] Optical (T, Δt) emits, from output 1216, the information pulsesalone without the activating (control) pulses. This emitting of theinformation pulses occurs only when the time delay Δt of (T, Δt) (switch1200) is equal to the time spacing between the information pulses andthe activating pulses related to each pair of pairs of pulses in beam1210.

[0239]FIG. 13 illustrates a group of graph 1300 demonstrating theprinciple of all-optical self-triggered CDM according to the invention.Graphs 1302 to 1310 of group 1300 illustrate the intensity I of ONE andZERO logical bits versus time t.

[0240] Graph 1302 shows time-envelope 1312 in which the logical data ofdifferent serial information channels can be placed. Time-envelope 1312does not contain any logical data; it shows only time slots 1314 inwhich pulses are allowed. Time-envelope 1312 is divided into equallength intervals T3. Each interval T3 contains a guard interval T2 thatis equal to or longer than T3/2. Guard interval T2 is a restricted timezone for any type of data and neither information nor control(activating or triggering) pulses are allowed during this period. A timeslot T4=T3−T2 is an interval during which data may be encoded. Timeperiod T4 is divided to K time pulse-slots 1314 having width T4/K=Δt.Each pulse-slot 1314 within envelope 1312 may contain a logical pulsehaving a width Δt.

[0241] As described with reference to FIG. 12, the code for activatingoptical switch 1200 of FIG. 13 includes a symbol representing data andan activating (controlling or triggering) pulse. These pulses areseparated by a time interval corresponding to a data particular channel.Each of the information channels gets its identity by its specific codedefined by the delay between the pulses making up the symbol. That is,the data for each different channel differs from the others by theunique time mΔt between the pair of pulses representing specific code,where m is an integer channel number. This method is a form of CDM witheach pulse spacing defining a unique channel. Alternatively, each uniquepulse spacing may represent a different data symbol.

[0242] Each time slot T4, with its pulse-slots 1314, may be reserved, inTDM fashion, for a TD channel or each time slot may be used for a singlechannel. For each time slot T4 only two pulses, each pair correspondingto one symbol, is provided in each slot T4. Since guard interval T2 isforbidden for any type of pulses, interval T3 can contain only twopulses as well.

[0243] Envelope 1312 of graph 1302 may contain multiple codes ofmultiple information channels interleaved serially with the time in anydesired order.

[0244] For example, graph 1304 illustrates serial data stream 1322including pulse pairs 1316, 1318, and 1320 of three different TDchannels. Pulse pairs 1316, 1318, and 1320 each include two pulsesseparated by times 2Δt, 5Δt, and (k−1) Δt, respectively.

[0245] To demultiplex serial data stream 1322 of graph 1304 from asingle optical fiber into multiple parallel ports of optical fibers,each must contain only one information channel corresponding to thisport. Data stream 1322 may be split into multiple ports. To each port isapplied the signal 1322. For example, the signal 1322 may be applied tothe inputs of all-optical switch 1200 of FIG. 12. Switches 1200 eachcharacterized by a unique pair of parameters T and Δt.

[0246] Each of switches 1200 receives at its input 1202 the entire datastream including the codes of all the information channels. Each switch1200 detects and emits, at its output, pulses only for data in the inputdata stream code corresponding to the code channel for which the switchis constructed. Thus, in this design, each of output ports 1204 ofswitches 1200 will emit only the information pulses of one informationchannel from the serial of channels of graph 1304.

[0247] Graph 1304, illustrates data stream 1322. All switches 1200receive this data stream at their inputs 1202. Thus this graph alsoillustrates the data stream of beams 132 inside switches 1200, asdescribed above in the explanation of FIG. 12.

[0248] Graph 1306 illustrates data stream 1322 of graph 1304 with a timedelay of 2Δt. As explained above for switch 1200, this graph mayillustrate the data stream of control beam 134, inside switch 1200, withthe switch having a delay of 2Δt. Thus it is characterized by the vector(T, 2Δt). In this particular case, since the pulses 1316, 1318, and 1320have a width T equal to Δt, the switches are characterized by: (Δt,2Δt). Note that strictly-speaking, the descriptor (T, Δt) is not fully acharacterization of the switch in that Δt merely constrains the choicesof T and T is chosen a priori for use with a given switch. The switchitself is characterized by its internal delay which is indicated fullyby Δt.

[0249] Arrows 1324 show that only the first pulse of code 1316 in graph1306 has a complete time overlap with the second pulse of code 1316 ingraph 1304. Graphs 1304 and 1306 also illustrate the pulses of beams 132and 134, respectively. This means that inside this specific switch 1200there is also a similar time overlap between the pulses of beams 132 and134. Thus, only the information pulse of code 1316 will appear at output1204 of switch 1200. Output 1204 is characterized by (Δt, 2Δt). Codes1318 and 1320 do not produce, in this switch, any time overlap betweentheir pulses in corresponding beams 132 and 134; Thus none of theirpulses appears in the output of switch 1200.

[0250] Accordingly, in general, switch 1200 has a delay 2Δtcharacterized by (Δt, 2Δt). Switch 1200 emits only the information pulsefrom the two-pulse code of the information channel. It does so only whenthis code includes two pulses that are separated by a time space 2Δt.The pulses of other codes, separated by a time space equal to theintegral number of Δt that differs from 2Δt, will not be emitted byswitch 1200 and will not appear at its output.

[0251] Similar to graph 1306, graph 1308 illustrates data stream 1322 ofgraph 1304 with a time delay of 5Δt. As explained above for switch 1200,this graph actually also illustrates the data stream of control beam134, inside switch 1200 when this switch has a delay of 5Δt. Thus it ischaracterized by (T, 5Δt). In fact since the pulses also have a width Tequal to Δt, the switch is characterized by (Δt, 5Δt).

[0252] Arrows 1326 show that only the first pulse of code 1318 in graph1308 has a complete time overlap with the second pulse of code 1318 ingraph 1304. Graphs 1304 and 1308 also illustrate the pulses of beams 132and 134 inside switch 1200, characterized by (Δt, 5Δt), respectively.This means that in this switch there is also a similar time overlapbetween the pulses of beams 132 and 134. Thus, only the informationpulse of code 1318 will appear at output 1204 of switch 1200,characterized by (Δt, 5Δt). Codes 1316 and 1320 do not produce any timeoverlap between their pulses in corresponding beams 132 and 134. Thusnone of their pulses appear in the output of switch 1200 characterizedby (Δt, 5Δt).

[0253] Accordingly, in general, switch 1200 has a delay 5Δtcharacterized by (Δt, 5Δt). It detects only the information pulse fromthe information channel whose code includes the two logical pulses thatare separated by time 5Δt. The pulses of other codes that are separatedby a time equal to integral number of Δt that differs from 5Δt will notbe detected by switch 1200 and will not appear at its output.

[0254] Similar to graphs 1306 and 1308, graph 1310 illustrates datastream 1322 of graph 1304 with a time delay of (k−1)Δt. As explainedabove for switch 1200, characterized by (Δt, 2Δt) and (Δt, 5Δt), thisgraph actually also illustrates the data stream of control beam 134,inside switch 1200 when this switch has a delay (k−1)Δt. Thus it ischaracterized by (T, (k−1)Δt). In fact since the pulses also have awidth T equal to Δt, the characterization takes the form (Δt, (k−1)Δt).

[0255] Arrows 1328 show that only the first pulse of code 1320 in graph1310 has a complete time overlap with the second pulse of code 1320 ingraph 1304. Graphs 1304 and 1310 also illustrate the pulses of beams 132and 134 inside switch 1200, characterized by (Δt, (k−1)Δt),respectively. This means that in this switch there is also a similartime overlap between the pulses of beams 132 and 134. Thus, only theinformation pulse of code 1320 will appear at output 1204 of switch1200, characterized by (Δt, (k−1)Δt). Codes 1316 and 1318 do notproduce, in this switch any time overlap between their pulses incorresponding beams 132 and 134. Thus none of their pulses appear inoutput 1204 of switch 1200 related to (Δt, (k−1)Δt).

[0256] Accordingly, in general, switch 1200, has a delay (k−1)Δtcharacterized by (Δt, (k−1)Δt). It detects the information pulse onlyfrom the information channel whose code includes the two pulses that areseparated by time (k−1)Δt. The pulses of other codes are separated by atime equal to an integral number Δt that differs from (k−1)Δt. They willnot be detected by switch 1200, characterized by (Δt, (k−1)Δt), and willnot appear at its output 1204.

[0257] Accordingly, each switch 1200, out of all switches 1200 that arefed in parallel by the split information of the coded serial channels,will detect only the information pulses from the code whose two pulsesare separated by a time equal to the delay of the switch. Thus switches1200 convert the serial coded channels propagating in a single opticalfiber into parallel channels, each of which propagates in differentparallel optical fibers.

[0258] While FIG. 13 illustrates only three channels represented bytheir codes 1316, 1318, and 1320, the serial channels can contains k−1different channels (for any desired k). These k−1 channels can bedivided, as explained above, from propagating in a single fiber topropagate in multiple parallel fibers, each of which contains only theinformation pulses from a different information channel.

[0259] Guard interval T2 is a forbidden time zone from which the logicalpulses are restricted. Guard interval T2 is needed to avoid unwantedtime overlap between the pulses of different codes that exist ininformation carrier beam 132 and control 134 inside switches 1200. In asituation when guard interval T2 does not exist, the time delay betweenbeams 132 and 134 could cause time overlap between the pulses ofdifferent codes in beams 132 and 134. Such overlap could cause mixingand crosstalk between the divided different information channelspropagating in parallel fibers, which should be isolated from eachother.

[0260] Interval T3 contains only one pair of pulses and actually onlyone pulse of this pair represents an information pulse (or, putdifferently, each pulse pair represents only one symbol). Interval T3 isat least 2 k times longer than the width Δt of the symbol. Accordingly,this method of multiplexing may seem at first to be inefficient in termsof information density. In practice, however, according to the inventionand as illustrated by FIG. 7c and explained above in its description,the pulses can be produced with width T that is very narrow. Pulse widthT can be produced, according to the invention, to be so narrow thatinterval T3=2 k·T still will be much shorter than any pulse widthproduced by the modulators known today. Accordingly, a very dense serialstream of information channels can be used with the symbology method forwhat is here defined as Dense Time division Multiplexing\deMultiplexing(DTDM). The combination of the high density of information that can beachieved with the DTDM with the ultra high switching speed of thesymbology makes the use of the DTDM very attractive for use in opticalnetworks for transmitting a large volume of information at a high rate.

[0261] The optical system that actually performs the principle of thesymbology, illustrated by the graphs of FIG. 13, is illustrated by FIG.14, discussed below.

[0262]FIG. 14 schematically illustrates a self-triggered Code DivisionMultiplexing (CDM) system 1400 that is used for DTDM (Dense TimeDivision Multiplexing). Demultiplexing optical system 1400 is theoptical system that practically performs a CDM method based on thesymbology illustrated in FIG. 13. System 1400 has a single input 1402 towhich optical fiber 1408 is optically coupled. Information carrier beam1418 enters fiber 1408 through its input 1416 and propagates along fiber1408 to be coupled to system 1400 at input 1402. Input 1402 couplesinformation carrier beam 1418 into fiber 1403. Beam 1418 propagates infiber 1403 toward optical node (junction) 1406. Node 1406 can be aone-to-many coupler. It divides single information carrier beam 1418into k−1 information carrier beams 1420 that propagate along opticalfibers 1206. Each of beams 1420 contains all the information exists incarrier beam 1418. Each of fibers 1206 connects node 1406 to switch1200, which is of the type illustrated in FIG. 12 and which has input1202 and output 1204.

[0263] Switches 1200 are differ from each other only by theircorresponding delay parameter and thus are indicated by theircorresponding parameters. The delay parameters of the (k−1) switches1200 have values that are integral number of Δt and create a serieshaving serial different Δt's that starting with Δt and end with (k−1)Δt.Arrows 1410 represents those of switches 1200 that are not shown in FIG.14.

[0264] Information carrier beam 1418, propagating in a single fiber1408, includes a serial data stream that includes k−1 differentinformation channels interleaved between each other in any desiredserial order. Beam 1418 has a time envelope 1312 (FIG. 13). Thus itspulses may occupy each of time slots 1314 in time period T4 of envelope1312 of FIG. 13 in a configuration that time period T2 is devoid of anypulse. Similar to graph 1304 of FIG. 13, the codes of the differentinformation channels are formed by their corresponding pairs of pulses.They are formed in a configuration where only one code is related to aspecific information channel and exists during time period T4 ofenvelope 1312. Each code includes one information pulse and one controlpulse for a single data symbol.

[0265] The time lag between the two pulses of each of code is related toa particular information channel. The time lag varies from one channelto another and has a specific value that corresponds uniquely to arespective information channel. The interval between the two pulses ofthe (k−1) different codes have values that are integral multiples of Δtand define a series starting with Δt and end with (k−1)Δt.

[0266] All the codes of the information channels that informationcarrier beam 1418 carries arrive at inputs 1202 of switches 1200 throughfibers 1206 and by beams 1420 into which beam 1418 is divided. Beams1420 carries all the codes of the information channels that beam 1418carries. These codes are applied to switches 1200 via their respectiveinputs 1202.

[0267] Each of the switches 1200 detects and transmits to its output1204 only when the code in the information channel corresponding to itsinternal delay. I.e., it only transmits pulses for the codecorresponding to the particular switch 1200 in which the pulses in eachcode are separated by a time interval equal to the time delay of theswitch 1200. Neither the information pulse nor the activating pulse ofthe codes of other channels not corresponding to as given switch 1200produces a pulse at the its output 1204. Accordingly, the informationpulses for each code are output only by a respective information channeloutput 1412.

[0268] The information pulse of each code is represented by one of thetwo pulses that define the code. Each of switches 1200 receives, at itsinput 1202, various codes of different information channels. From thesevarious codes switch 1200 detects and transmits to its output 1204 onlythe information pulse of the code that is related to the specificinformation channel. In this case the time interval between the twopulses of the code is equal to the delay parameter of this specificswitch 1200.

[0269] For example, (k−1) optical switches 1200 are indicated by their(T, Δt), (T, 2Δt), (T, 3Δt), (T, 4Δt), and (T, (k−1) Δt). These switcheswill transmit to their outputs 1204 only the information pulses from the(k−1) codes that correspond to that are separated by time intervalsequal to Δt, 2Δt, 3Δt, 4Δt, and (k−1)Δt respective thereto.

[0270] The information pulses of the different information channel arecoupled by different outputs 1204 of switches 1200 into different fibers1404 and are carried by different beams 1414 that are from respectiveoutputs 1412 of system 1400.

[0271] Accordingly, optical system 1400 defines an all-optical Codedivision Multiplexing (CDM) system. System 1400 receives, in its singleinput 1402, a series of multiple coded information channels interleavedin any desired order. System 1400 emits, from its multiple outputs 1412,only the information pulses of the different coded information channels.These information pulses are fed into its input 1402, when each of thedifferent information channels exits, by a demultiplexing process, froma different output 1412 without any crosstalk between the channels.

[0272]FIG. 15a illustrates how modulator and switch 1200 of FIG. 12 isused to produce ultra narrow pulses 1508 of beam 1212 at output 1204.

[0273] Modulator 1200 receives in its input 1202, through optical fiber1206, information carrier beam 1210 that is coupled to fiber 1206 intoits core 1214. Arrow 1506 indicates that pulse 1502 is related to beam1210 and has a width T. As explained above, beam 1210 is divided intocarrier beam 132 and control beam 134 inside modulator 1200. Carrierbeam 132 includes all the information of beam 1210 and thus pulse 1502also represents beam 132. Control beam 134 is delayed by a time delayΔt, as illustrated by pulse 1504 that is time shifted by Δt, relative topulse 1502 of beam 132, and has the same width T as pulse 1502.

[0274] The time overlap T−Δt between pulses 1502 and 1504 of beams 132and 134, respectively, produce narrow pulse 1508 at output 1204 ofmodulator 1200, that has a width T−Δt.

[0275] Pulse 1508 at output 1204 of modulator 1200 is coupled intooptical fiber 1208 and is emitted, by beam 1212, from fiber 1208 throughits output 1216, as is illustrated by arrow 1510.

[0276] The delay values Δt of modulator 1200 can be adjusted as desiredand thus Δt can be chosen to produce pulse 1508 with an extremely narrowwidth T−Δt.

[0277] Accordingly modulator 1200 receives radiation pulses 1502 thatcan be produced in a conventional way by conventional radiation sourcesand modulators. These pulses are converted, by modulator 1200 into ultranarrow pulses 1508. These pulses are much narrower than the pulsesproduced by any known modulating technique.

[0278] Modulators, such as modulator 1200, can be placed in the opticalpath of parallel information channels to convert their pulses into muchnarrower pulses. Due to the narrow width of the new pulses in theseparallel information channels, they can be interleaved to a serial datastream by standard DTM techniques. This stream will have a much higherinformation density, so as to produce DTDM. This serial pulse steam ofthe above mentioned DTDM should be demultiplexed by the fastest standardtechniques known today.

[0279] In addition to the DTDM, narrow pulses, such as pulse 1508produced by modulator 1200 or any other modulator according to theinvention, can also be used to increase the information density of anyother communication method, such as WDM or DWDM.

[0280] The all-optical CDM according to the invention should havespecial codes. These codes should be encoded, by multiplexing, into theserial interleaved data stream of the DTDM to allow the multiplexing byCDM technique of the invention. FIG. 15b, described below, illustratesan interleaving or multiplexing system according to the invention thatis also capable of encoding the symbols needed for the demultiplexing bythe CDM technique of the invention.

[0281]FIG. 15b illustrates a system 1520 for encoding, by multiplexing,the specific codes according to the invention, of multiple parallelschannels 1522 that are interleaved into serial data stream for TDM,DTDM, CDM, WDM, and DWDM, Asynchronous Transfer Mode (ATM), DenseAsynchronous Transmitting Mode (DATM), or any other application ofoptical communication, including packet routing.

[0282] System 1520 has multiple inputs 1526 and a single output 1528.Parallel information channels 1522, represented by their informationpulses 1524, are fed into inputs 1526 of system 1520. Pulses 1524 arethe shortest pulses that can be achieved today. Pulses 1524 are cut bylines 1530 to indicate that, in spite of their narrow width, theirlength is still much longer than that illustrated.

[0283] Inputs 1526 of system 1520 are coupled into nodes 1532. Nodes1532 that receive radiation pulses 1524 of channels 1522 divide thisradiation equally into optical fiber 1534 and optical fibers 1536. Thebeams from fibers 1534 and 1536 are fed into inputs 1202 of modulators1200.

[0284] Modulators 1200 produce very short pulses 1544 at their outputs1204. Each of pulses 1544 is accompanied by arrow 1545 that indicates inwhich fibers pulses 1544 propagate. The width Δt=T−Δt1 of pulses 1544depends upon width T of pulses 1524 and delay time Δt1 of modulators1200 ((T, Δt1). Modulators 1200 are arranged in (K−1) pairs, startingwith pair 1538 through pair 1540 to pair 1542. Broken arrows 1538represent the pairs of modulators 1200 that are not shown in FIG. 15.

[0285] Pulses 1544 at outputs 1204 of modulator pair 1538 are coupledinto optical fibers 1546 and 1548, respectively. Pulses 1544 at outputs1204 of modulator pair 1540 are coupled into optical fibers 1550 and1552, respectively. Similarly, pulses 1544 at outputs 1204 of modulatorpair 1542 are coupled into optical fibers 1554 and 1556, respectively.

[0286] Delay fibers 1558, 1560, and 1562 in fibers 1546, 1550, and 1556produce time delays corresponding to the specific codes of modulatorpairs 1538, 1540, and 1542, respectively. For example, delay fibers1558, 1560, and 1562 produces delays of Δt, 2Δt, and (K−1)Δt,respectively. Index (K−1) represents the number of modulator pairs usedwhen the (K−1)th pair is pair 1542.

[0287] Node 1564 receives pulses 1544, having width Δt, from fibers 1546and 1548. Node 1564 combines these two pulses and emits them, throughsingle fiber 1570, on the other side of node 1564. Pulses 1544 of fibers1546 and 1548 have a width Δt and are delayed by time interval Δt. Thuswhen combined into fiber 1570, they produce a specific code pair 1576corresponding to modulator pair 1538, that includes two pulses that areshifted by Δt.

[0288] Node 1566 receives pulses 1544 from fibers 1550 and 1552. Node1566 combines these two pulses and emits them, through single fiber1572, on the other side of node 1566. Pulses 1544 of fibers 1550 and1552 have width Δt and are delayed by interval 2Δt. Thus when they arecombined into fiber 1572, they produce specific code pair 1578corresponding to modulator pair 1540, that includes two pulses that areshifted by 2Δt.

[0289] Similarly, node 1568 receives pulses 1544 from fibers 1554 and1556. Node 1568 combines these two pulses and emits them through singlefiber 1574, on the other side of node 1568. Pulses 1544 of fibers 1550and 1552 have a width Δt and are delayed by time interval (K−1)Δt. Thuswhen are combined into fiber 1574, they produce a specific code pair1580, corresponding to modulator pair 1542, that includes two pulsesthat are shifted by (K−1)Δt.

[0290] Specific codes 1576, 1578, and 1580 of modulator pairs 1538,1540, and 1542 are accompanied by arrows 1582, 1584, and 1586 thatindicate fibers 1570, 1572, and 1574 in which they propagate,respectively.

[0291] Fibers 1570, 1572, and 1574 include delay fibers 1588, 1590 and1592, respectively. Delay fibers 1588 to 1592 represent a series of(K−1) delay fibers corresponding to (K−1) modulator pairs 1538 to 1542.The time delays that delay fibers 1588 to 1592 produce are an integralnumber of time periods T3, shown in FIG. 13. These delays create amathematical series having a serial difference T3 that starts with adelay T3 and ends with a delay (K−1)T3 for first and last delays 1588and 1592, respectively.

[0292] Fibers 1570, 1572, and 1574 are connected to node 1594, which hasonly a single output 1528 that is also the output of system 1520. The(K−1) specific codes 1576 to 1580 of the (K−1) information channels 1522that are coupled to (K−1) inputs 1526 of system 1520 propagate in (k−1)fibers 1570 to 1574. These codes enter node 1594 with time differencesT3 between them. Node 1594 combines (K−1) codes 1576 to 1580 into aserial data stream that consists of codes 1576 to 1580 that areinterleaved in every time period T3. Beam 1596 that exits from output1528 of system 1520 carries the serial data stream produced by node 1594that interleaves (k−1) codes 1576-1580 in serial of codes spaced by atime shift T3. Nodes 1564-1568 can be two-to-one couplers and node 1594can be a many-to-one coupler Arrow 1598 indicates that the series ofpulses that beam 1596 carries is represented by the pulses confined intime-envelope 1312, similar to time envelope 1312, illustrated in FIG.13. Time envelope 1312 includes time cells 1602 having width T3 anddefined as code cells 1602. Each code cell 1602 includes restricted timezones 1604 and occupied time zone 1606. The occupied time zone is a timeperiod that can be used to transmit the codes pulses. The widths ofrestricted time zone 1604 and occupation time zone 1606 are T2 and T4,respectively. Width T2 is greater or equal to T3/2.

[0293] Any of occupation zones 1606 contains only one code out of (k−1)codes 1576-1580. Since occupation zones 1606 may include any of (k−1)codes 1576-1580, their size T4 must be great enough to allow them tocontain even the longest code that has a width Δt(K−1)Δt=KΔt.Accordingly, the time length of time zone 1606 is T4=KΔt.

[0294] Codes 1576-1580 are interleaved in (k−1) code cells 1602, whereeach code cell 1602 contains only one specific code related to itsspecific information channel 1522. Codes 1576-1580 are arranged in aseries of (k−1) cells. These cells are arranged in a multiplexing orinterleaving order that starts with code 1578 and ends with code 1580.Specific codes 1576-1580 are used in all-optical demultiplexing system1400, illustrated in FIG. 14.

[0295] System 1400 receives cells 1602 and includes switches 1200 thatproduce a time shift between their inside beams, carrier beam 132 andcontrol beam 134. The maximum time shift between beams 132 and 134,inside switches 1200 of system 1400, is illustrated by FIG. 14. It canreach a value of (K−1)Δt. To avoid any mixing and crosstalk between thecodes in cells 1602, any time overlap between the different pulses ofdifferent codes 1576-1580 in cells 1602 of beams 132 and 134 should beavoided. Such over lap can be avoided if the separation time T2 betweencode cells 1602 is grater than the maximum shift (K−1)Δt between beams132 and 134 inside switches 1200 of system 1400. Accordingly T2 is equalto or longer than (k−1)Δt. Since T3=T2+T4, it is equal toKΔt+(K−1)Δt=(2K−1)Δt and thus T2 is approximately longer than or equalto T3/2.

[0296] The total length 1608 of all (k−1) code cells 1602 isT5=(K−1)T3=(K−1) (2K−1)Δt. When T2 is equal to T4=2 kΔt, then T5=(K−1)(2k)Δt. The time length T5 is the time that system 1520 of FIG. 15b isbusy in producing code cells 1602. Thus system 1520 is free to get thenext period of pulses, from information channels 1522 in its inputs1526, only after time period T5.

[0297] Accordingly, system 1520 operates at a frequency rate of I/T5.The width of pulses 1524 in information channels 1522 is much largerthan the width of the pulses in codes 1576-1580. Thus there is asignificant time saving using the system of 1520 with respect tostandard TDM system.

[0298] Compression Factor Of DTDM With Respect To Standard TDM-FIG. 15b

[0299] Compression factor C is defined as the ratio between the averagebit rate exists in DTDM as, illustrated by FIG. 15b, and conventionalTDM, as used today.

[0300] According to the invention and as illustrated in FIG. 15b, eachcode cell 1602, in the DTDM method, carries two pulses, but, assumingone bit per symbol for purposes of discussion, only, only oneinformation bit. Accordingly, for a time period T5, that includes (k−1)codes cells 1602, the number of interleaved information pulsestransmitted is (K−1). Thus the average bit rate R1 in the DTDM is:

R1=(k−1)/T5=(k−1)/[(k−1) (2K)Δt]=½KΔt

[0301] In a standard TDM the interleaved pulses, such as the pulses ofinformation channels 1522, have width of T. Thus for transmitting (K−1)pulses, the time needed is (K−1)T. Accordingly, the average bit rate R2is:

R2=(k−1)/(K−1)T=1/T

[0302] Compression factor C equal to:

C=R1/R2=T/2KΔt

[0303] For example, the width Δt of the pulses in codes 1576-1580 caneasily produced to be 1000 times shorter than the width T of standardpulses, as produced and used in present TDMs. Assuming that K the numberof information channels interleaved in both methods DTDM and TDM is 50then:

C=1000Δt/2·50·Δt=10

[0304] This means that, by using the DTDM method, the bit rate caneasily be increased by a factor of 10.

[0305] Achieving compression factor C=10, by the DTDM method with theadditional capability of ultra fast all-optical demultiplexing makes theDTDM a very attractive method.

[0306] When using DTDM with very short pulses, according to theinvention, and interleaving them, by the standard TDM method withoutencoding codes (as done when using CDM), the compression factor C can bemuch higher. The need to encode the interleave pulses to be used, inall-optical self-triggering CDM, reduces compression factor Csignificantly.

[0307] For example, when producing, according to the invention, pulsesthat are 1000 times shorter than available today, by other techniques,and interleaving them by a standard TDM technique, without CDM, thencompression factor C is 1000. On the other hand, such a high pulse ratecannot be demultiplexed using known techniques; demultiplexing by theCDM technique of the invention is required.

[0308] The all-optical switching capabilities of system 1400 of FIG. 14are per single code corresponding to a single information pulse. Whenthe DTDM method is used to interleave packets of information, the codecells of the same packets are arranged in arrows, one after the other.All of the cells of the same packet have the same specific code and thusall will be routed to the same port. Accordingly, all-opticaldemultiplexing system 1400 is also capable of routing packets. System1400 can serves as one junction for routing packets. For routing packetsthrough more than one junction, the specific codes should include moreinformation to define the routing path through multiple junctions. Suchcodes will be discussed in the following section.

[0309]FIG. 15c schematically illustrates all-optical system 1700representing an all-optical communication network. System 1700 includessystem 1520 of FIG. 15b, that serves as an encoding or multiplexingsystem, and system 1400 of FIG. 14, described above, that serves as ademultiplexing system.

[0310] Systems 1520 and 1400 are connected by single long-haul fiber1702 that transmits a serial data stream of radiation pulses. A longhaul is a long information carrier designed to carry multipleinformation channels for transmitting large information volume, at highrate, between junctions of the communication network. System 1520 hasmultiple parallel inputs 1526 through which it receives pulses 1524 ofmultiple parallel information channels 1522. Pulses 1524 are cut bylines 1530 to indicate that pulses 1524 are longer than as illustrated.System 1520 produces specific codes corresponding to respective channels1522; each code consist of a pair of pulses.

[0311] As illustrated in FIG. 15b, these specific codes areall-optically interleaved, by multiplexing system 1520, in any desiredpredetermined order to form series of code pairs 1596 that exit fromsystem 1520 through its output 1528. Data stream 1596 is coupled, byconnector 1704, to a single long-haul fiber (backbone) 1702 throughwhich it propagates toward connector 1706. Connector 1706 couples datastream 1596 into input 1402 of demultiplexing system 1400.

[0312] As illustrated in FIG. 14, system 1400 receives the series of theinterleaved specific codes of channels 1522, produced by multiplexingsystem 1520, and all-optically demultiplexes only the information pulsesof these codes into and from its parallel outputs 1404. The informationpulses of the specific codes related to different information channels1522 are carried by beams 1414 and exit from different subsidiaryoutputs 1412 related to main outputs 1404 of system 1400.

[0313] Referring now to FIG. 16A, the mechanism for taking a(temporally) broad pulse 1337 or 1338, such as used in current opticalsystems, is processed to make the pulses much narrower. The resultingpulses may be interleaved with appropriate delay circuits discussedbelow to create a high bandwidth signal. Presently, the process forencoding a broad-pulse signal of the prior art to encode it with routingdata for one or more layers of routing (e.g., layers of the system 1400)is described. The system discussed now with reference to FIG. 16A is analternative to that discussed with reference to FIG. 15b and is shown inthe present context simply to illustrate another means by which thepulse-pair encoding may be achieved.

[0314] An input data stream 1340 is applied to an optical splitter 1341which may be a directional coupler or Y-junction, to send energy inequal intensity to a gate 1352 such as described with reference to FIG.12 (there shown at 1200). It is assumed that the circuiting indicated bybroken lines in the diagram leading from the splitter 1341 to the gate,have appropriate delays such that the delay between the portion of thepulse arriving at one input of the gate 1352 is delayed by preciselyΔt_(c), a result that is schematically represented as a delay device(e.g., a delay line) at 1354. By applying each broad pulse 1337 and 1338to both inputs of the coincidence gate 1352 with a time delay Δt_(C),only the portion overlapping in time is transmitted to the output. As aresult, the output signal 1348 that emerges has a width Δt_(B) equal tothe difference between the delay Δt_(C) and original pulse width Δt_(D).The spacing Δt_(A) between the successive output symbols 1337′ and 1338′remains the same as in the original signal.

[0315] Each of many signals such as signal 1348 can then be applied toan optical summing device, such as a Y-junction or other device (seebelow for discussion of Y-junctions, directional couplers, etc.) tocreate a high density time-multiplexed signal. Alternatively, an opticalamplifier can be used to amplify the signals either in their originalform 1338 or at a later stage after chopping and interleaving. WhileFIG. 16A shows a method of narrowing the pulses width, demultiplexing isa problem. This is addressed by encoding the signal in the mannerdiscussed with respect to FIG. 13. Encoding system 1520 illustrated byFIG. 15b demonstrates an encoding process. Another means by which thisencoding may be accomplished is to route the pulses through multiplelayers, which is discussed with reference to FIGS. 16B to 16D.

[0316] The output signal 1348 from the previous figure may be applied toa duplicator circuit 1372. The latter is simply an optical splitter 1365and a delay device 1367 configured to split the signal 1348 and sum adelayed copy 1366 of the signal with a non-delayed copy 1364. Here thedelay is indicated as having a magnitude of Δt₃. The output signal 1362retains the original symbol spacing. As should be clear from theforegoing discussion and particularly that attending FIG. 14, when“routed” by a receiving coincidence gate, the control/information pulsedisappears. To allow the pulse-pair to contain routing information formultiple layers, the pulse-pair must contain enough information to routethe pulses through the next layers in spite of the loss of pulses in therouting process through the previous layers. In this situation thepulse-pair contains multiple pulse-pairs and the original signal 1348 isreproduced in a corresponding channel by a repeating a process similarto that performed by duplicator 1372.

[0317] Note that the distance between adjacent pulses Δt_(A) isillustrated as being very large in this example. As discussed above, theallowed range of spacings between pulses, which corresponds to thenumber of degrees of freedom of the code, should preferably not violatethe minimum guard band rule, unless some other means is employed tofilter out unwanted interference, a matter not discussed in the presentdisclosure. In the present example, the spacing Δt_(A) is illustrated asrelatively large in anticipation of adding multiple layers of encoding,which is discussed next.

[0318] Referring now to FIG. 16C, the pulse-pair symbology may beapplied to multiple router layers of coincidence gate-based switchessuch as system 1400 of FIG. 14. To accomplish this, the pulse pairencoding the destination for a symbol is treated as a single pulse andreproduced, as were the pulses of the original data stream 1348 in thedescription attending FIG. 16B. The signal 1362 is applies to anotherduplicator circuit 1374 with another time delay Δt₂. This time delay Δt₂corresponds to the delay of a level of coincidence gate switch system(e.g. 1400) that would precede the switch layer configured to routebased on the time delay Δt₃. That is, Δt₃ Is the interval that specifiesa coincidence gate switch in the final layer of routing systems 1400 andΔt₂ is the interval that specifies a coincidence gate switch in thepenultimate layer of routing systems 1400. An upper layer of routingencoding may be added as illustrated in FIG. 16D. Here, each set ofpulses making up each symbol in signal 1366 is reproduced at anappropriate interval spacing by another duplicator circuit 1376configured with a delay of Δt₁. The encoding represented by the intervalΔt₃ would be the last to be processed and routed by the last layer(highest layer) of routing switch systems (e.g., 1400) that includesmultiple routing layers.

[0319] Referring now to FIG. 16E, signal 1368 is annotated with certaindetails to help clarify the above discussion. Each set of four pulses inthe interval 1384 represents a single symbol from the original sourcesignal 1340 encoded by the duplicator circuits 1372, 1374, and 1376.Each of the time intervals Δt₁, Δt₂, and Δt₃, selects a uniquecoincidence gate switch (e.g. 1200 in a system including multilayersystems of FIG. 14) in a given layer of switch systems (e.g., 1400 inFIG. 14). Each output of a switch, such as CDM system 1400, in a firstlayer, corresponds to a unique value of Δt₁. Each output of a switch ina second layer, corresponds to a unique value of Δt₂. Each output of aswitch in a third layer, corresponds to a unique value of and Δt₃.

[0320] The time slots available for encoding the highest layer codesrange over an interval 1396. The slots are spaced at least a pulse widthapart (and are at least a pulse-width wide) The series of adjacent slotsmust be defined such that they occupy a time range that is no wider thaninterval 1396. A corollary is that Δt₃ should never be outside this timerange 1396.

[0321] The time slots available for encoding the penultimate layer codesrange over an interval 1394. The slots are spaced apart by at least theinterval 1396. The slot widths are at least at least the interval 1396.The series of adjacent slots must be defined such that they occupy atime range that is no wider than interval 1394. A corollary is that Δt₂should never be outside the time range 1394.

[0322] The time slots available for encoding the antepenultimate orinitial layer codes range over an interval 1392. The slots are spacedapart by at least the interval 1394. The slot widths are at least atleast the interval 1396. The series of adjacent slots must be definedsuch that they occupy a time range that is no wider than interval 1392.A corollary is that Δt₁ should never be outside the time range 1394.

[0323] A guard interval 1390 must maintain a distance between adjacentinitial switch layer slot ranges that is at least as great as interval1392 to prevent intersymbol interference. The guard zone requirementonly exists at the highest layer of encoding. This is because the timedelays that correspond to the lower layers is always a fraction of thoseat higher layers, the presence of the highest level guard interval 1390guarantees that no overlap will occur between successive symbols in thelower layers.

[0324] Refer now to FIG. 16F, which illustrates further how themultilayer signal is processed through multiple layers. The originalsignal (e.g. 1368 from FIG. 16D) here shown at 1605, is applied to afirst layer 1601 of switches 1200A-1200F each with a respective timedelay Δt_(a)-Δt_(f). Switch 1220C, which is within the range of switches1200A-1200F (a range which has an arbitrary number of switches withinthe confines of the encoding range), outputs signal 1606 because it isconfigured for the matching time interval Δt₁. The signal 1606, may bethought of as containing the structure of one half of the signal 1605and results due to the coincidence effect described for coincidencegates above. The other switches in the layer 1601 output no signal,because their time delays have non-matching values.

[0325] Signal 1606 is applied to the second layer of switches1200N-1200R, each with a respective time delay Δt_(n)-Δt_(r). Switch1220P, which is within the range of switches 1200N-1200R (a range whichalso has an arbitrary number of switches within the confines of theencoding range), outputs signal 1607 because it is configured for thematching time interval Δt₂. The signal 1607, may be thought of ascontaining the structure of one half of the signal 1606 and results dueto the coincidence effect described for coincidence gates above. Theother switches in the layer 1602 output no signal, because their timedelays have non-matching values.

[0326] Signal 1607 is applied to the third layer of switches1200V-1200Z, each with a respective time delay Δt_(v)-Δt_(z). Switch1220×, which is within the range of switches 1200V-1200Z (a range whichalso has an arbitrary number of switches within the confines of theencoding range), outputs signal 1608, because it is configured for thematching time interval Δt₁. The signal 1608, may be thought of ascontaining the structure of one half of the signal 1607 (or a singlepulse) and results due to the coincidence effect described forcoincidence gates above. The other switches in the layer 1603 output nosignal, because their time delays have non-matching values.

[0327] Note that in FIG. 16F, the shapes of the pulse patterns are notnecessarily to scale.

[0328]FIG. 17 illustrates how WDM may be combined with the symbologymethod of the present invention in a communications system. Multipleinstances of the interleaving/multiplexing system described withreference to FIG. 15b may be provided, for example as indicated at 1610.Each of the multiplexed channels may be assigned a frequency channel andmultiplexed in a WDM process 1620 for transmission on a long haulchannel 1615. Corresponding demultiplexing provided by a WDM demuxengine 1625 is provided at a receiving end, the respective frequencychannels of which may be applied to respective optical demultiplexers1626 and 1627, such as those illustrated in FIG. 14. Note that twolayers of demultiplexers are shown. These may employ the mechanism formultiple-layer encoding described with respect to FIGS. 16A-16D.

[0329] There are several conclusions and ramifications regarding thedetails of the above embodiments that may be summarized here beforediscussing some other types of interference devices that may beconfigured to provide coincidence gate-type functionality similar tothat discussed above. One of ordinary skill will observe that among theembodiments and inventions discussed, at least the following areprovided:

[0330] 1. All-optical modulators for generating ultra narrow pulses toproduce DTDM.

[0331] 2. Ultra fast all-optical switches.

[0332] 3. All-optical modulators and switches that are radiationcontrolled or are self-triggered.

[0333] 4. All-optical encoding symbology that may be used for datainterleaving or multiplexing with very narrow pulses that may beradiation controlled or self-triggered.

[0334] 5. All-optical decoding or demultiplexing systems that may beradiation controlled or self-triggered.

[0335] 6. Extremely fast all-optical systems for multiplexing anddemultiplexing and which may be used for DTDM.

[0336] 7. Extremely fast all-optical systems for multiplexing anddemultiplexing codes for CDM, self-routing, self-triggering, ATM, anddata routing.

[0337] 8. A method for modulating logical symbols that are self-routingwithout separate control data or packet headers.

[0338] 9. Novel devices that may be used for selectively directingoptical energy in cylinders within and outside the communications field.

[0339] The foregoing embodiments are by no means the only means by whichthe inventions discussed above may be implemented. Referring now to FIG.18, as will be discussed in some detail below, directional couplers, asillustrated for example at 1650, are interference devices of a sort inthe radiation applied to them interferes to produce various results attheir outputs. For example, respective light signals applied to theports indicated at 1 and 2 may interfere in a way that is determined bythe structure of the directional coupler 1650. The interaction of thesesignals dictated by the structure of the coupler, the phase and electricfield amplitude of the light incident on the ports 1 and 2 (as well asother factors) determines the electric field amplitude and phase of thelight emitted from ports 3 and 4.

[0340] As will be appreciated by persons of skill in the relevantfields, it is possible to create a directional coupler in which lightincident on port 1 will result in radiation signals being emitted fromports 3 and 4 which are equal in electric field amplitude with a π/2phase difference. More specifically, where the signal incident on port 1has an electric field amplitude of E, the signal emitted from port 3would have an electric field amplitude of E/{square root}{square rootover (2)} and in a certain phase relative to the input signal. Thesignal emitted from port 4 has the same field amplitude, but its phaseis π/2 radians ahead of that of the signal emitted from port 3. Theintensity of the signals is given by squaring the electric fieldamplitude so the port 1 signal has intensity I=E², and port 3 and 4signals have intensity I/2=E²2 or half that of the signal applied to theinput port 1.

[0341] For convenience, the following notation convention will beadopted. The intensity of light will be specified and where relevant,the phase indicated by multiplication by a symbol J to indicate a π/2phase difference, by −1 to indicate a π phase difference, and by −J toindicate a −π/2 phase difference. Thus, −J*I/2 means a signal whoseintensity is I/2 and whose phase is −π/2 ahead (or π/2 behind) of areference signal.

[0342] A quick review of the signals incident on waveguides 1655, 1660shows that when a signal is applied at port 2, the mirror-image obtainsat the output ports 3 and 4. That is, the signal at port 3 is J*I/2 andthat at port 4 is I/2. The more interesting situation occurs when lightof equal intensity is incident on ports 1 and 2, but different in phaseby −π/2. That is, the signal incident on port 1 is I and that on port 2is −J*I. The output at port 4 is zero. All of the energy incident onports 1 and 2 arrives at port 3. In this case, although shown, the phaserelationship between the energy at port 3 and that at port 4 isirrelevant since no light is emitted from port 4.

[0343] Referring now to FIG. 19, the effects of reverse Y-junctions oninput energy is discussed. When a light signal is applied to port 5 or 6of Y-junctions 1680 and 1685, respectively, the output intensity at port7 is half that of the applied at the input. When light is incident onboth input ports 5 and 6, of Y-junction 1690, simultaneously and in thesame phase, the output energy output at port 7 is half the total appliedat ports 5 and 6. In terms of the phase effects, where input signalsinterfere so that input signals of opposite phase cancel each other andsignals in phase add, with a 50% attenuation in intensity.

[0344] Referring to FIG. 20, coincidence devices 1700 and 1705 are eachformed from a pair of Y-junctions 1715 and 1730 and Y-junctions 1720 and1760 and a single directional coupler 1710 and 1725. Each device 1700and 1705 has a phase shifter 1740 and 1745 at a corresponding outputport 7 of each device 1700 and 1705. As may be determined by inspection,an identical signal at ports 1 and 5 of intensity I results in a signalat port 7 of I/2 and signals of equal intensity at ports 3 and 4, withthe signal at port 4 being shifted forward in phase by π/2 relative tothe others. A −π/2 phase shift is applied to the port 7 signal resultingin a signal of −J*I/2, which is of the same magnitude as the port 4signal but opposite in phase. This is applied at port 9 of Y-junction1730. The port 4 signal is applied to port 8 of the same y-junctionresulting in an output of zero at port 10.

[0345] The coincidence device 1705 experiences a similar cancellationeffect when signals of J*I and I are applied at ports 2 and 6, as may beconfirmed by inspection and with the aid of the symbols in FIG. 20.Thus, when these inputs are applied at the ports 2 and 6, a zero outputis obtained at the output port 10. Referring now to FIG. 21, when thesignals of FIG. 20 are applied to all the input ports 1, 2, 5, and 6,simultaneously, a very different result obtains, with the result beingan output of intensity and phase J*I/2.

[0346]FIG. 21 shows that port 4 carries a signal of high intensity,with, namely an intensity of 2*I with a phase of π/2 as it enters port 8of Y-junction 1785. The intensity at port 9 of Y-junction 1785, afterthe phase shifter 1780, is I with a phase that is opposite to that ofthe signal in port 8. The Y-junction 1785 combines the powers in ports 8and 9 according to their intensities and phases to produce an outputsignal at port 10 with an intensity of I/2. At the same time, under theabove conditions, nulling port 3 has zero output signal and all theenergy from port 3 is transferred to port 4. It can be seen that theratio between the intensities of port 4 in FIG. 21 and FIG. 20 is 4(2I/(I/2)=4).

[0347] Note that the notation in the drawings does not follow strictconvention. For example, the result obtained at port 10 is shown as amixture of intensity, which a scalar, and phase, which is a vector. TheY-junction 1785 may be configured, as is known in the art, so that itsoutput is half the sum of the intensities of its inputs with phasecancellation given by the interference of their waveforms. This meansthat where the inputs are opposite in phase, as is the case for inputsat ports 8 and 9, the output signal intensity is the difference of theinputs signal intensities attenuated by 50%. Where the input signals arein phase, the output is the sum of the intensities of the input signalsattenuated by 50%.

[0348] Note that the coincidence devices 1710, 1705, and 1770 may bemanufactured on a single substrate as waveguides. The phase shifters1740, 1745, and 1780 may be provided by simply heating a portion of thewaveguide material to change the refractive index. This could be donewith an ohmic heater or the like. Another way of forming the phaseshifters is to apply a voltage that creates a depletion region, a deviceknown as a Schottky contact. If the devices are made from opticalfibers, a pressure could be applied, for example, by means of apiezo-electric device, to change the index of refraction.

[0349] Note also that it should be obvious that some phase change willoccur as energy propagates along the waveguides in the forgoing devices.And this has been ignored in the discussion. So, for example, the phaseof the signal output at port 4 will not be identical to the phase as thesame signal is applied to port 8. Similarly, the phase differencebetween the signal at port 7 will not be precisely −π/2 radiansdifferent from that at port 9. Thus, the discussion has discussed theperformance of the devices in a somewhat schematic way, but in a realdevice a designer would have to account for propagation delays and theeffect these have on phase to insure that the desired results provide acoincidence effect such as that shown. In practice, this issue is adesign detail that may be ignored for purposes of discussion of theinventions and various embodiments thereof.

[0350] Note that the light applied to one pair of ports (either 1,5 or2,6), may regarded as a single signal input. The signal applied at theport 1,5 input is different, but equal in power to that applied to theport 2,6 input. The latter is an ordered pair with a predefined phasedifference that is always the same. When a signal is applied to oneinput without simultaneous application of a signal at the other, theoutput signal (port 10) is zero. When respective signals are applied atboth inputs, the output is equal to one fourth the power at either inputor an eighth of the total power applied to the inputs.

[0351] Because the port 2,6 input has a predefined phase difference fromthe phases of the other input signals, and because of the behavior ofthe coincidence device 1700, 1705, and 1770 noted above, it is possibleto construct coincidence gate with behaviors that are similar to that ofembodiments shown in FIG. 6b (an externally-triggered gate), for exampleand 1200 of FIG. 12 (a self-triggered gate).

[0352] Referring now to FIG. 22, a self-triggered coincidence gate shownin a coincidence state where an input signal applied at input port 12has a pair of pulses separated by a time interval that matches delaylines 1800 and 1801. The structure shown in FIG. 22, may be confirmed byinspection, to apply input signals to ports 1, 2, 5, and 6, that areidentical in terms of relative magnitude and phase to the signalscorresponding to the coincidence state illustrated in FIG. 21. If thetime interval Δt of the input signal applied at port 12 fails to matchthat of the delay lines 1800 and 1801, it may be confirmed by inspectionthat the result will be successive states of the system that coincidewith those illustrated in FIG. 20. The two possible noncoincidencestates obtain when the Δt of the input signal is different from that ofthe delay lines 1800 and 1801. In such cases, each pulse travels thoughthe gate 1810 without a corresponding pulse interfering with it inrelevant portions of the circuit as may be seen by inspection. That is,as illustrated in FIG. 23 when the first pulse passes through, passesthrough, a signal of intensity I passes through port 6 and one of J*Ithrough port 2′ (which corresponds to port 2 in FIG. 20) with nocorresponding pulse in ports 1 and 5. The result is the situation of thelower half of FIG. 20 where the output is zero. As illustrated in FIG.24, when the second pulse passes through, a signal of intensity I passesthrough ports 1 and 5 with no corresponding pulse in ports 2 and 6. Theresult is the situation of the upper half of FIG. 20 and the output iszero.

[0353] Note that although delay lines 1800 and 1801 (as well as delaylines and other devices illustrated in embodiments discussed below) areillustrated as elongated channels (E.g., in the present figure they aresuggested to be rolls of optical fiber, for example), various techniquesmay be used to produce the required delay. For example, materials inwhich light propagates more slowly (e.g., higher index of refractionachieved by doping) may be added so that the path need not be undulyelongated. Even some kind of energy conversion process likeoptical-electrical-optical could be used if delays are permitted to berelatively long. Such a device would act as a store-and-forward bufferbut with current energy conversion technology, it would be usable foronly very long delays. However, there some applications would permitthis.

[0354] Referring to FIG. 25, a design essentially the same as that ofFIGS. 22-24 may be based on the use of a star-splitter 1840 rather thanthree Y-junctions as in the embodiments of FIGS. 22-24. The lengths ofthe radiation guides arms of star-splitter 1840 are preferably designedto assure that the all the radiations enters the ports 1, 2, 5, and 6with the same phase (or equivalently such that the phase at which theenter the points is appropriately compensated further on such that theultimate result of a coincidence-gate function is obtained). It shouldbe clear from the illustration that such an embodiment would behave in amanner that is equivalent to the embodiments of FIGS. 22-14.

[0355] Thus, it is clear that the behavior of the coincidence gate 1810is essentially the same as that of gate 1200. However, the total energyloss of the gate 1810 may be substantially higher than that of gate1200. We assumed in the above discussion that the gate 1200 is based onthe embodiments of FIGS. 1-11d, although the discussion of gate 1200 andthe modulation techniques discussed in connection with FIGS. 12-17 applyequally to embodiments such as gate 1810 and other embodiments to bediscussed below.

[0356] Referring now to FIG. 26, another self-triggering coincidencegate-type device illustrates some concepts that may be used for makingdevices based on waveguide technologies and also some more generalconcepts. For example, a gate could be fabricated using lithographytechniques using such an approach. For example time delays may beprovided in appropriate locations with an alternative to the fiberoptical delay lines suggested by the images of delay devices 1800 and1800 and 1801 of FIG. 22. Instead, a delay line, preferably ofhigh-refractive index material, in the form of an elongated waveguideachieved by, for example, serpentine path portions 1905 and 1910 of thecircuit, may be provided as indicated. These portions may be of amaterial with a higher index of refraction than the material used inother parts of the device so that the lengths of the serpentine pathsportions 1905 and 1910 may be minimized for convenience. However, thisis not necessary.

[0357] Another feature of the disclosed embodiment is that instead ofusing Y-junctions, star splitter, or a star coupler, a series of 50%/50%directional couplers 1920, 1925, and 1930 (known also as 3 dB couplers)are used in a manner similar to that of the embodiments of FIGS. 22-24.In this case, however, the directional couplers inherently introduce arelative phase difference of π/2 radians in the outputs which must beaccommodated in the design. In the schematic illustration, the signal atport 2 differs in phase from that at port 1 (when simultaneous signalsplace the device in the coincidence state) without the need for anadditional phase shifter.

[0358] Recall that these are only schematic illustrations and inpractice, the structure of the design (including path lengths andmaterials) may inherently provide the phase shifting. For example, theserpentine delay portion 1905 or other types of delay devices such asdelay lines 18001 and 1801 (shown in FIG. 22), introduces multiple phaserotations and if designed to do so, can insure that the correct relativephase angles are provided at the various interference portions of thedevices to obtain the desired result.

[0359] Note also that there is another phase rotation introduced bydirectional coupler 1930 and yet another by directional coupler 1925.The end result is that to achieve the desired interference effect in thecoincidence device portion 1930 (i.e., the relative phase angles at theinput ports 1, 2, 5, and 6), a phase rotation of −π/2 radians is appliedin the lower branch 1916 of directional coupler 1925. The result is thatthe inputs at ports 1, 2, 5, and 6 produce the constructive interferenceeffect at port 4 so that all the energy applied at ports 1 and 2emanates at port 4, but the phase angles emitted at port 7 needs to berotated by −π before being applied to the Y-junction 1945 in order toproduce the coincidence-type output at port 10. Note that only thecoincidence state is shown in connection with the embodiment of FIG. 26,however it may be confirmed by inspection that the structure producesthe correct behavior under noncoincidence conditions.

[0360] Note that the use of directional couplers instead of Y-junctionsresults in a lower energy loss through the entire system. That is, onemay be see that the energy loss through the embodiment of FIGS. 22-24 isa factor of 32, while the energy loss through the embodiment of FIG. 26is only by a factor of 8. The losses in the device of FIG. 26 may becompensated for by an optical amplifier 1950 at input port 1965.

[0361] Referring now to FIG. 27, another alternative mechanism forcreating a coincidence gate device is illustrated here. A star splitter1960 is configured to output an input optical signal applied at inputport 1965 to each of four ports 1970 with equal intensity and phase. Thetraveling time from the input port 1965 of star splitter 1960 to eachport of the pair of ports 1 and 5 (of ports 1970) is assumed in thisexample to be the same. Similarly, The traveling time from the input ofstar splitter 1960 to each port of the pair of ports 2 and 6 (of ports1970) is also assumed to be the same. The energy loss with the starsplitter 1960 is less than with the cascade of Y-junctions of theprevious embodiment with the input energy being equally divided amongthe outputs. As known by those of skill in the relevant arts, such astructure may be created via current design techniques. In theembodiment of FIG. 27, serpentine portions are used for delay as in theembodiment of FIG. 26. In all other respects, the embodiment of FIG. 27is essentially as the embodiment of FIG. 25.

[0362] Note that although in the embodiment of FIG. 27, the time delayof all the branches of the star splitter 1960 was assumed to be thesame, in practice this, of course, need not be true as long as thecoincidence effects required are obtained. For example, the delays oftime delayers 1967 and 1968 may be incorporated totally or in part incorresponding branches of the star splitter 1960.

[0363] It should be clear from the above that there are a wide varietyof ways of generating the coincidence-gate functionality fromdirectional couplers and/or Y-junctions in various combinations.

[0364] Referring now to FIG. 28, another way to form a coincidence gatetype functionality is by the use of certain features of beam splitters.Illustrated in FIG. 28 are dielectric beam splitters which have thefollowing properties. An incident beam 2010 incident in a firstdirection on a dielectric beam splitter 2025 is divided into a reflectedbeam 2015 and a transmitted beam 2020, each with an intensity that ishalf that of the input beam. The phase angle of the reflected beam 2015is π/2 greater than that of the transmitted beam 2020. The samesituation obtains when an incident beam 2030 is incident from anotherdirection on the dielectric beam splitter 2025. That is the incidentbeam 2030 is divided into a reflected beam 2035 and a transmitted beam2040, each with an intensity that is half that of the incident beam 2030with the phase angle of the reflected beam 2035 being π/2 greater thanthat of the transmitted beam 2040.

[0365] When incident beams 2010 and 2030 are coincident from theirrespective directions on the dielectric beam splitter 2025, with theindicated phase relationships, they interfere constructively. The resultis a coincidence effect at the output beam 2045 from the reflectiondirection of incident beam 2010 and the transmitted direction ofincident beam 2030. That is, in the reflection direction of incidentbeam 2010 and the transmitted direction of incident beam 2030, thecombined energy output is four times that when either of the incidentbeams 2010 and 2030 is incident by itself.

[0366] The coincidence effect can be used to generate zero and non-zerooutputs in noncoincident and coincident states, respectively byproviding optical circuits that provide a magnitude slicing function asprovided in previous embodiments discussed above. A number of examplesare discussed below with regard to FIGS. 34-42. First, a few moreexamples of coincidence devices are discussed.

[0367] Referring now to FIG. 29, metallic beam splitters have thefollowing properties. An incident beam 2050 incident in a firstdirection on a metallic beam splitter 2025 is divided into a reflectedbeam 2055 and a transmitted beam 2060, each with an intensity that is aquarter that of the input beam. The phase angle of the reflected beam2055 is n greater than that of the transmitted beam 2060. The samesituation obtains when an incident beam 2070 is incident from anotherdirection on the metallic beam splitter 2065. That is the incident beam2070 is divided into a reflected beam 2075 and a transmitted beam 2080,each with an intensity that is a quarter that of the incident beam 2070with the phase angle of the reflected beam 2075 being 7 greater thanthat of the transmitted beam 2080.

[0368] When incident beams 2050 and 2070 are coincident from theirrespective directions on the metallic beam splitter, with the indicatedphase relationships, they interfere constructively and no loss occurs inthe metal film (not shown separately). The result is a coincidenceeffect at the output beam 2085 from the reflection direction of incidentbeam 2050 and the transmitted direction of incident beam 2070. That is,in the reflection direction of incident beam 2050 and the transmitteddirection of incident beam 2070, the combined energy output is fourtimes that when either of the incident beams 2050 and 2070 is incidentby itself.

[0369] The embodiment of FIG. 29 is another example of how a beamsplitter can be used to make a coincidence device. The behavior plays arole in the various devices described above and below. This is the casealso with the early embodiments using the transmitting and reflectinggratings as described above with reference to FIGS. 2-11. That is,referring now to FIG. 30, the zero lobe may be regarded as an outputwhich is indicated as an output 2110 at port 2. As discussed above, theoutput 2110 energy incident at port 2 is a fourth that of the incidentbeam when either of the input beams at ports 1 or 5 is incident on agrating 2100 alone. When both are coincident on the grating 2100simultaneously, the energy in the zero order lobe, indicated as anoutput 2115 at port 2, is only half that of the total energy incident.Thus, the energy at the output 2 in the coincidence state is four timesthat in the noncoincidence state.

[0370] Referring now to FIG. 31 and recalling the discussion of FIG. 19,it may be confirmed immediately that the Y-junction exhibits acoincidence behavior, albeit less markedly in terms of intensity. Thatis, in either noncoincidence state, the output is half that of thecoincidence state. The energy loss in all states is about 50%. Nofurther explanation of FIG. 19 is given since the concepts werediscussed with reference to FIG. 19.

[0371] The same “power combiner” behavior as exhibited by the Y-junctionof FIGS. 19 and 31 is exhibited by another device shown in FIG. 32. Apair of mirrors 220 directs either of two incident beams 2230 and 2245toward an optical fiber receiver 2220 via a lens 2210. An output beam2225/2240 is proportional to the energy incident on the mirror 2200. Inthe two noncoincident states, the output is the same intensity as theinput multiplied by a constant of proportionality. When both beams arecoincident, the output is the combined incident power multiplied by thesame constant of proportionality. As in the previous embodiment, theratio of output during the coincidence state to that during thenoncoincidence state is a factor of two.

[0372] Another kind of power combiner that may be used to produce thesame effect is a reflecting/transmitting grating with very high pitchrelative to the wavelength of light incident thereon. No diffraction,and therefore no interference fringes, are produced because thewavelength of light is substantially greater than the grating spacing.However, inspection of FIG. 33 highlights the similar behavior to thatof a metallic beam splitter with the phase rotation of an incident beam2310 occurring for a reflected beam 2305 and no phase rotation occurringfor a transmitted beam 2300. However, the attenuation of the metallicbeam splitter in noncoincidence states is not present intransmitting/reflecting grating 2315, and thus it functions more as a“power combiner” and not as a coincidence device as does metallic beamsplitter does. In other respects, the behavior of such a grating issubstantially identical to that of a metallic beam splitter for purposesof the coincidence behavior and a discussion of the details is thereforenot provided again.

[0373] Referring now to FIG. 34, a coincidence gate that produces zerooutput in noncoincidence states and a nonzero output in the coincidencestate has a two part first input signal provided by either the controlor data signal (again, using the illustrative terminology of “control”and “data” employed for purposes of discussing the embodiments)indicated 2345 and 2350. For example, the signals that arrivesimultaneously to ports 1 and 6 are provided by either the control ordata signal and similarly, the signals that arrive simultaneously toports 2 and 5 are provided by either the data or control signal,respectively. These have non-identical phases which may be derived byany suitable means such as a phase shifter or by suitable delayrelationships in input circuitry (not shown here, but exemplified inother embodiments discussed above and below as should be clear in thedetailed description of the embodiments). The first part 2345 of theinput signal is partly reflected by the beam splitter 2340 and partlytransmitted resulting in beams 2355 and 2347. Although shown, therelative phases of these signals has no relevance, but the phase ofsignal 2347 must be opposite one produced by the other part 2350 of theinput signal via the circuit including Y-junction 2365 and phase shifter2360. That is, the result of the combination of the signals at ports 8and 9 by a final Y-junction 2370 should be zero.

[0374] Referring now to FIG. 35, an the alternative noncoincidencestate, the embodiment of FIG. 34 receives the other of the data orcontrol signals in two parts 2351 and 2346. These two parts may haveidentical phases which may be derived by any suitable means such as aphase shifter or by suitable delay relationships in input circuitry (notshown here, but exemplified in other embodiments discussed above andbelow as should be clear in the detailed description of theembodiments).

[0375] Note that the phase relationships between the two parts (here andin FIG. 34) is arbitrary so long as suitable design is provided in otherparts of the circuit such that the correct interference interactionoccurs. But the relative phases of input signal 02346 and 2351 isimportant to insure that the beam splitter's output to port 4 in thecoincidence state is much greater in magnitude than that produced by thepower combiner 2365 as discussed with regard to FIG. 36, below, whichshows the coincidence state.

[0376] Returning to the discussion of the noncoincidence state of FIG.35, the first part 2346 of the input signal is partly reflected by thebeam splitter 2340 and partly transmitted resulting in beams 2356 and2348. Again, the structure must insure that the phase of signal 2348 isopposite that produced by the other part 2351 of the input signal viathe circuit including Y-junction 2365 and phase shifter 2360. That is,the result of the combination of the signals at ports 8 and 9 by a finalY-junction 2370 should be zero.

[0377] Referring now to FIG. 36, when respective parts 2345 and 2346 ofboth the data and control signals are incident on the beam splitter2340, all the energy of the two signals emerges at port 4 as a signal2375. The phase of this signal 2375 is the same as that in each of thenoncoincidence states, but it is four times the magnitude, that is, 2I.The Y-junction combines the other parts 2350 and 2351 of the data andcontrol signals, but the resulting intensity is only twice that in thenoncoincidence states of FIGS. 34 and 35. Thus, when combined with thesignal in the Y-junction 2370, a non-zero output 2380 at port 10 isobtained.

[0378] In terms of the relative intensity, the behaviors of the deviceof FIGS. 34-36 is essentially the same as that described with respect toFIGS. 20 and 21. To apply signals to the various inputs of the device ofFIGS. 34-36, the same input circuitry 1993, 1994, 1995, and 1996 (shownin FIGS. 22-27) as added to corresponding parts (i.e., applied at ports1, 2, 5, and 6) to the device of FIGS. 20 and 21 may be used. That is,the input circuit portions 1993, 1994, 1995, and 1996 may be used aswell as variations thereof discussed above and the wide variety othersthat may be envisioned based on the principles presented herein.

[0379] Note that although the above embodiment of FIGS. 34-36 included adielectric beam splitter 2340, it is clear that other types of devicesmay be used to achieve the same effect. For example, a metallic beamsplitter could be substituted, with appropriate circuiting to providethe required phase relationships as illustrated by FIG. 29.

[0380] Referring now to FIG. 37, the present embodiment is similar tothat of FIGS. 34-36 except that a different power combiner 2420 of thetype discussed relative to FIG. 32 is used and the input signal portionsapplied to it indicated (schematically) to have an input phase that is nahead of that provided in the embodiments of FIGS. 34-36. That is, aportion 2351′ of one of the data and control signals has an initialphase of 7. Again, as should be clear, the input phases are arbitrary solong as the circuitry design provides appropriate interaction withincomponents where the signals interfere.

[0381] The power combiner 2420 includes a mirror pair 2410, a lens 2405,and a receiving port 2425 of an optic fiber. The signal 2351′ isattenuated by the insertion process, but is proportional to the initialsignal and is shown at port 7 with an intensity of I/2 and a phase thatis n ahead (or behind) that at port 4, as symbolized by the multiplier−J. The port 4 signal is as in the previous embodiments. Anattenuator/amplifier 2415 is included to indicate that the circuitryneeds to ensure the output of the Y-junction 2370 is zero.

[0382] Referring now to FIG. 38, the complementary one of control anddata signals is applied in respective portions 2345 and 2350′ to theports 2 and 6, respectively with the same result as in FIG. 37 with azero output at port 10 of the Y-junction 2370.

[0383] Referring now to FIG. 39, as in the coincidence state illustratedin FIG. 36 and the attending discussion, when respective parts 2345,2346 of both the data and control signals are incident on the beamsplitter 2340, all the energy of the two signals emerges at port 4 asthe signal 2375. Here again, the phase of this signal 2375 is the sameas that in each of the noncoincidence states, but it is four times themagnitude, that is, 2I. The Y-junction combines the other parts 2350′and 2351′ of the data and control signals, but, as with the embodimentof FIGS. 34-36, the resulting intensity is only twice that in thenoncoincidence states of FIGS. 37 and 38. Thus, when combined with thesignal in the Y-junction 2370, a non-zero output 2381 at port 10 isobtained. Again, as before and although it hardly bears repeating, thephase of the final output 2381 is arbitrary and will depend on theprecise details of the design and may even depend on the environmentalconditions.

[0384] Referring now to FIG. 40, yet another kind of energy combiner maybe used with the circuit portions of the embodiment of FIGS. 34-36common to that of FIGS. 37-39. The combiner in this embodiment is a zeroorder grating 2460 as discussed above with regard to FIG. 33. Here, asin FIG. 35, the first and second portions 2351 and 2346 either of thedata signal or the control signal are applied simultaneously to thepower-combiner zero order grating 2460 at the equivalent port 5 and tothe beam splitter 2340 at port 1. The results are identical to thoseshown in FIG. 35 and discussed with respect thereto. That is, theemerging signal applied at port 7 is phase-shifted to oppose the signalapplied at port 8 with the result that the port 8 and 9 signalsinterfere in the Y-junction 2370 and output essentially no signal atport 10. The common features are not discussed again, since they shouldbe clear from the discussion of FIGS. 34-39.

[0385] Referring now to FIG. 41, the complementary signals either fromthe data signal or from the control signal are applied simultaneously atports 2 and 6 with a similar result that is essentially as describedwith respect to FIG. 34. Finally, referring to FIG. 42, in a coincidencestate, a non-zero output 2382 is obtained for reasons that should beclear from the previous discussion of previous embodiments. In theembodiment of FIGS. 40-42, the zero order grating 2460 acts as an energycombiner just as the Y-junction 2365 and the power combiner 2420. Thecommon elements of FIGS. 40-42 need not be described again since theyfunction essentially as described in previous embodiments to produce asimilar result. As with the embodiment of FIGS. 34-36 to apply signalsto the various inputs of the device of FIGS. 37-39 and that of FIGS.40-42, the same input circuitry 1993, 1994, 1995, and 1996 (shown inFIGS. 22-27) as added to corresponding parts (i.e., applied at ports 1,2, 5, and 6) to the device of FIGS. 20 and 21 may be used. That is, theinput circuit portions 1993, 1994, 1995, and 1996 may be used as well asvariations thereof discussed above and the wide variety others that maybe envisioned based on the principles presented herein.

[0386] Principles of some of the foregoing embodiments may be extendedto other embodiments easily in view of the following abstraction. Inmany of the foregoing embodiments, each of two signals is combined, in afirst process, to produce a first output of a first power level and in asecond process to produce a second output of a second power level. Thefirst and second processes are such that the same signals individuallyare combined in the first and second processes to produce, respectively,a third output at third power level and a fourth output at the samethird power level. The third and fourth outputs are caused to interferein a third process such that they cancel. The first and second outputsare also caused, by the same third process to cancel, but the thirdprocess of cancellation is such that, because the first output is at ahigher power level than the second, residual energy remains after thecancellation process. Thus, when both signals are processed to producefirst and second outputs, a non-zero output is obtained. When eithersignal is processed alone, no output is obtained.

[0387] Referring to FIG. 43, to illustrate the above abstraction, thefirst process is represented here as a black box labeled“augmentation/cancellation process 1500.” The latter has one or moreoutputs. The augmentation/cancellation process 1500 is such that the oneor more outputs have a combined power that is a higher proportion of thetotal input power when both signals 1 and 2 are incident than wheneither signal 1 or 2 is incident alone. Examples of these are thedirectional coupler, dielectric or metallic beam splitter, and aspectsof the transmission/reflecting grating and spatial interference device800.

[0388] Referring to FIG. 44, the second process is represented here as ablack box labeled “power combiner 1510.” The latter has one or moreoutputs. The power combiner process 1510 is such that the one or moreoutputs have a combined power that is proportional to the total inputpower when both signals 1 and 2 are incident as well as when eithersignal 1 or 2 is incident alone. Examples of these are the reverseY-junction, the zero order grating, and the power combiner of FIG. 32.Referring now to FIG. 45, a power combiner, which may be identical tothe power combiner 1510, combines outputs 1 and 2 such that the output 3is proportional to the combined power of the inputs if the two outputsinterfere constructively and which is zero if the two signals have thesame intensity and interfere destructively. As a result of thenonlinearity of the signal levels at output 1 of theaugmentation/cancellation process 1500 as a function of the signalarrangement in inputs 1 and 2, the power level of output 3 can, byjudicious design of the processes 1500 and 1510 and/or processing of theoutputs 1 and 2, be made to result in a zero output 3 when input signals1 and 2 are incident alone and produce at output 1 a signal to be equalto output 2 but of a character that when combined in power combiner 1520they cancel (e.g., have an opposite phase). A nonzero output 3 resultswhen input signals 1 and 2 are incident simultaneously and produce anoutput 1 that is greater than output 2 (coincident state).

[0389] While the above description contains many details, these shouldnot be considered as limitations on the scope of the invention, but asexamples of the presently preferred embodiments thereof. Many otherramifications and variations are possible within the teachings to theinvention.

[0390] For example the all-optical switches, modulators, encoding anddecoding systems, interleaving and multiplexing systems, anddemultiplexing systems have been described for use in communicationnetworks. However they can be used in other optical systems as well,such as systems used for optical computing. They also can be used asoptical components, devices, and systems in Ethernet systems. Althoughthe invention been described using the examples of DTDM andself-triggered CDM it can be used for producing very narrow pulses toperform standard techniques, such as TDM, ATM and packets routing.

[0391] Although the some systems have been described as modulators theyalso can be operated as switches. While some all-optical encoding andmultiplexing systems have been described using sub-units operating asmodulators, the situation can be reversed, i.e., the operation of thesesame sub-units can be change to serve as switches in decoding anddemultiplexing systems. Though some switches and modulators have beendescribed with one output they can include multiple outputs. While themodulators and the switches have been described as containing gratingsor phase arrays, they can also include another interference devices thatare capable of changing their pitch according to the illuminationconditions. Although the gratings and the phase arrays have beendescribed as having one ore three interference orders, they are notlimited to these numbers of interference orders. While some of theswitches and the modulators are illustrated without optical amplifiersthey can be integrated with optical amplifiers, such as a Europium DopedOptical Fiber Amplifier (EDOFA).

[0392] Thus the scope of the invention should be determined by theappended claims and their legal equivalents, and not by the examplesgiven.

[0393] It will be evident to those skilled in the art that the inventionis not limited to the details of the foregoing illustrative embodiments,and that the present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A multiplexed optical communication system comprising: means forproducing very narrow optical pulses in different parallel channels;means for multiplexing the very narrow optical pulses of the differentparallel channels into a single serial bit stream; means fortransmitting the single serial bit stream at a very high bit rate; meansfor demultiplexing, at a very high speed, the single serial bit streamback into different parallel channels.
 2. The multiplexed opticalcommunication system of claim 1 wherein the means for producing verynarrow optical pulses in different parallel channels comprises means forproducing very narrow optical pulses from relatively wide opticalpulses.
 3. The multiplexed optical communication system of claim 1wherein the means for multiplexing the very narrow optical pulses of thedifferent parallel channels into a single serial bit stream comprisesmeans for delaying at least some of the very narrow optical pulses. 4.The multiplexed optical communication system of claim 1 wherein themeans for transmitting the single serial bit stream at a very high bitrate comprises an optical fiber.
 5. The multiplexed opticalcommunication system of claim 1 wherein the means for demultiplexing, ata very high speed, the single serial bit stream back into differentparallel channels comprises means for delaying.
 6. A method of opticalcommunication comprising: producing very narrow optical pulses indifferent parallel channels from relatively wide optical pulses;multiplexing the very narrow optical pulses of the different parallelchannels into a single serial bit stream, the multiplexing comprisingdelaying at least some of the very narrow optical pulses; transmittingthe single serial bit stream at a very high bit rate over a longdistance with an optical fiber; demultiplexing, at a very high speed,the single serial bit stream back into different parallel channels. 7.The method of claim 6 wherein producing very narrow optical pulses indifferent parallel channels from relatively wide optical pulsescomprises destructively interfering relatively wide optical pulses. 8.An all-optical multiplexing system comprising: a first bit pair sourcecomprising: a first input adapted to receive a first wide informationpulse; a first divider adapted to divide the first wide informationpulse into first and second wide pulses; a first modulator adapted toreceive the first wide pulse, the first modulator having a firstmodulator output adapted to output a first narrow pulse based on thefirst wide pulse; a second modulator adapted to receive the second widepulse, the second modulator having a second modulator output adapted tooutput a second narrow pulse based on the second wide pulse; a firstdelayer in communication with the first modulator output and adapted todelay the first narrow pulse by a time Δt and output a delayed firstnarrow pulse; a first pulse combiner adapted to combine the delayedfirst narrow pulse with the second narrow pulse and to output a firstpair of bits shifted by XΔt, where X is an integer; a second bit pairsource comprising: a second input adapted to receive a second wideinformation pulse; a second divider adapted to divide the second wideinformation pulse into third and fourth wide pulses; a third modulatoradapted to receive the third wide pulse, the third modulator having athird modulator output adapted to output a third narrow pulse based onthe third wide pulse; a fourth modulator adapted to receive the fourthwide pulse, the fourth modulator having a fourth modulator outputadapted to output a fourth narrow pulse based on the fourth wide pulse;a second delayer in communication with the third modulator output andadapted to delay the third narrow pulse by a time YΔt and output adelayed third narrow pulse, where Y is an integer and not equal to X; asecond pulse combiner adapted to combine the delayed third narrow pulsewith the fourth narrow pulse and to output a second pair of bits shiftedby YΔt; and a third delayer adapted to delay the second pair of bits bya time T₃ and to output a delayed second pair of bits; and a bitcombiner adapted to combine the first pair of bits with the delayedsecond pair of bits and to output a single serial data stream includingthe first pair of bits separated by T₃ from the delayed second pair ofbits.
 9. The all-optical multiplexing system of claim 8 wherein T₃ is atleast twice as long as 2Δt.
 10. The all-optical multiplexing system ofclaim 8 wherein the first, second, third, and fourth narrow pulses areat least about one thousand times shorter than the first wide pulse andthe second wide pulse.
 11. The all-optical multiplexing system of claim10 wherein the single serial data stream has a bit rate at least aboutten times faster than a bit rate associated with the first wideinformation pulse and the second wide information pulse.
 12. Theall-optical multiplexing system of claim 11 wherein single serial datastream has a bit rate at least about one thousand times faster than abit rate associated with the first wide information pulse and the secondwide information pulse.
 13. An all-optical code-division demultiplexingsystem comprising: a one-to-many coupler adapted to receive a singleserial optical input stream containing first and second codedinformation and to divide the single serial optical input stream into aplurality of information carrier beams each containing all theinformation that exists in the single serial optical input stream, theplurality of information carrier beams including a first informationcarrier beam and a second information carrier beam; a first opticalswitch adapted to receive the first information carrier beam and tooutput only the first coded information; and a second optical switchadapted to receive the second information carrier beam and to outputonly the second coded information.
 14. The all-optical code-divisiondemultiplexing system of claim 13 wherein: the first optical switchcomprises a first delayer adapted to delay the first information carrierbeam by an amount QΔt; the second optical switch comprises a seconddelayer adapted to delay the second information carrier beam by anamount RΔt; and Q and R and are integers and Q is not equal to R. 15.The all-optical code-division demultiplexing system of claim 13 whereinthe first optical switch comprises a first interference device and thesecond optical switch comprises a second interference device.